Ittan-momen (一反木綿, "one bolt (tan) of cotton") are yōkai (supernatural beings) in the folklore of Kōyama, Kimotsuki District, Kagoshima Prefecture (now Kimotsuki). They are also called ittan monme or ittan monmen.

According to the Ōsumi Kimotsukigun Hōgen Shū (大隅肝属郡方言集), jointly authored by the locally born educator Nomura Denshi and the folkloricist Kunio Yanagita, at evening time, a cloth-like object about 1 tan in area (about 10.6 metres (35 ft) in length and 30 centimetres (12 in) in width) would flutter around attacking people.

They are said to wrap around people's necks and cover people's faces and suffocate people to death, and in other tales it is said that wrapped cloths would spin around and around and quickly come flying, wrap around people's bodies, and take them away to the skies.

There is a story where one man hurrying to his home at night when a white cloth came and wrapped around his neck, and when he cut it with his wakizashi (short sword), the cloth disappeared, and remaining on his hands was some blood.

In regions where they are said to appear and disappear, there seemed to be a custom where children were warned that if they play too late, that "ittan momen would come."

Also, it is said that in Kimotsuki, there are shrines (the Shijūkusho Jinja [ja] for example) where ittan momen are said to frequently appear, and it was believed that when children pass in front of the shrine, an ittan momen flying above in the skies would attack the last child in line, so children would go run ahead and cut through.

In the classical yōkai emaki, the Hyakki Yagyō Emaki [ja], there is a yōkai shaped like a cloth with arms and legs. The folklorist Komatsu Kazuhiko [ja] hypothesizes that this is the origin of ittan momen.

According to a report from the yōkai researcher Bintarō Yamaguchi [ja], there have been claims of flying cloth-shaped objects said to be ittan momen.