To wear and remove an assist instrument has been difficult because a user has to wear or remove the assist instrument on or from her/his body in a state that an elastic member is contracted. An assist instrument comprises: an assist unit that is attached wearably and removably to a body of a user, and assists muscular strength of the user by at least one of extension and contraction； and a wearing-removal control unit that controls the assist unit at a time of at least one of wearing and detachment of the assist unit to extend the assist unit.
