In psychoanalytic theory, the term psychic apparatus (also psychical apparatus, mental apparatus) refers to the mental structures and mechanisms of the psyche. In Freud's 'topographical' model of the psyche, it refers to three systems – the Unconscious, the Pre-conscious, and the Conscious. In his later 'structural model', Freud described the psychic apparatus in terms of the id, ego and super-ego.

The apparatus, as defined by Freud, includes pre-conscious, conscious, and unconscious components. Regarding this, Freud stated:

We assume that mental life is the function of an apparatus to which we ascribe the characteristics of being extended in space and of being made up of several portions [Id, ego and super-ego].

— Freud, An Outline of Psychoanalysis (1940)

As a psychologist, Sigmund Freud used the German terms psychischer Apparat and seelischer Apparat, about the functioning of which he elaborates:

We picture the unknown apparatus, which serves the activities of the mind, as being really like an instrument constructed of several parts (which we speak of as 'agencies'), each of which performs a particular function, and which have a fixed, spatial relation to one another: it being understood that by 'spatial relation'—'in front of' and 'behind', 'superficial' and 'deep'—we merely mean, in the first instance, a representation of the regular succession of the functions.

— Freud, The Question of Lay Analysis (1926).

Freud proposed the psychic apparatus as solely a theoretic construct explaining the functioning of the mind, and not a neurologic structure of the brain.