A movement assistance device is provided with thigh frames, lower leg frames, and knee joint mechanisms which are disposed on the outer side and the inner side, respectively, of each knee of a person to be assisted. Each of the thigh frames has a first main frame, which extends in the longitudinal direction of a thigh from a base disposed on one side of the hip of the person to be assisted to the outer knee joint mechanism, a second main frame, which obliquely extends on the front side of the thigh from the base to the inner knee joint mechanism, and a body support member, which is extended between the two main frames on the rear surface side of the thigh.