A motion assist device, comprises a brace (2, 3, 5, 6, 11; 23, 24, 32, 35) configured to be worn by a user, an assist motor (4, 34) provided in association with the brace to assist a prescribed motion of the user, a control unit (10; 40) for controlling an operation of the assist motor, and an attitude detection sensor (8, 18; 38) connected to the control unit for detecting an attitude of the user. The control unit is configured to activate the assist motor when a prescribed attitude of the user is detected by the attitude detection sensor so that loads on parts of the user's body other than the part which is directly assisted can be minimized