An assist device includes: a first harness to be fitted to at least one of a shoulder region and a breast region of a user; a second harness configured to be fitted to one of a leg region and a waist region, of the user; a belt body provided so as to extend to the first harness and to the second harness along a back side of the user; an actuator provided in one of the first harness and the second harness; and a controller performs operation control of the actuator. The actuator winds a part of the belt body and unwinds the part of the belt body. The controller performs the operation control of the actuator based on a posture change of the user.