In sumo wrestling, a shimpan or shinpan (審判) is a ringside judge seated around the dohyō (sumo ring) to observe the match, identifying which wrestler wins the matchup and supervising the work of the in ring referee (called gyōji), to ensure that no refereeing errors are made.

Historically, the role of judge developed in the 18th century to facilitate arbitral decisions, which were subject to external pressures, before establishing itself as the ultimate decision-making authority at the end of the 19th century. In professional sumo, all judges are former wrestlers who have acquired the status of toshiyori (sumo elder) and have been assigned to the corresponding department within the Japan Sumo Association. During sumo tournaments (called honbasho), five judges sit around the dohyō, with additional elders serving as video review officials in another room. The judges command an aura of respect, reinforced by their formal, sober attire and the weight of their decisions.

The judges' main role is to ensure that all preparations for the matches are completed properly and on time, before assisting both the referee in the ring in deciding the outcome of a match and the referees on announcing duty in recording the winning techniques. If the outcome of a match is disputed, it is up to the judges to call a mono-ii to discuss the referee's decision, assisted by video refereeing.

However, the role of referees is not limited to matches. Behind the scenes, they are also responsible for establishing the banzuke, the ranking system that serves as the cornerstone of professional sumo. When wrestlers are eligible for promotion to the two highest ranks in the hierarchy (yokozuna and ōzeki), it is also their responsibility to ask the Sumo Association's board of directors to promote those selected, with their opinion serving as the basis for the promotion process and their recommendations never being ignored. Judges also serve as guardians of the etiquette associated with professional sumo, and it is their responsibility to enforce the rules and reprimand wrestlers and masters who violate them. Finally, they are responsible for organizing the matches, a role they perform every day of a tournament.

The elders' judging function developed around 1750, with the emergence of interests linked to the prestige of local lords. The fairness of the decisions handed down by the gyōji was increasingly called into question, because lords sponsored wrestlers. This led to the questioning of the gyōji's absolute authority over match results and the introduction of a system of judges, all elders, then called naka aratame (中改; ascertainers in the middle) but more commonly known as shihon bashira (四本柱; lit. 'four pillars'). This name was derived from their positions during matches, right at the base of the poles holding up the roof of the ring. Initially, the judges sat at the foot of the ring, but from around 1780 onwards, they took their places directly on the fighting platform. Three judges were led by a head judge, who had total authority and whose personal decision could not be questioned.

With Takasago Uragorō's return to the Tokyo Sumo Association, a series of reforms were implemented to satisfy his demands. One of these was to transfer the final say in the judgment of a disputed match from the referees (gyōji) to the judges. The judges took on the official name of kensayaku (検査役; inspectors). The office of judge evolved in the mid-20th century, with the removal of the powers of the head judge in 1958, considered too powerful and autocratic. With a final reform taking place in 1968, judges finally adopted the name shimpan (or shimpan-iin). The system for electing judges that had been in place until then was also abolished in favor of the system that remains in place today. The idea of bringing in judges who were not toshiyori but former wrestlers who showed little promise, retired and trained by their peers to become judges following the gyōji system, was considered but not implemented.

All judges are former wrestlers who have attained the status of toshiyori and have been assigned to the dedicated department of the Japan Sumo Association. Like all departments, the Judging Department is headed by a director assisted by a deputy. Starting with the 2020 March tournament, two toshiyori, with the status of director and deputy, were also attached to the department to focus solely on match scheduling and banzuke decisions. They will generally not serve as judge during matches, but will act as substitutes if the heads of the departments are unable to perform their role. The appointed toshiyori serve in the department for a one-year term, and their supervisors serve for a two-year term.

The number of judges is set between twenty and twenty-three, and places are distributed equitably among the various ichimon, or clans, within the association. Around the ring, the five judges all belong to a different clan. Initially, this difference between clans explained why judges interacted little with each other after matches, simply going home immediately after finishing their duties. Today, however, it is accepted that judges from the same team chat amiably and go out together to forge bonds.