A motion assist device includes a drive mechanism that applies a force to the body of a user through the intermediary of a first orthosis and a second orthosis, posture detectors that detect the posture of the user, and a control unit that controls the drive mechanism. A transmission mechanism of the drive mechanism is configured to be switchable between a transmission mode, in which a driving force based on a spring is transmitted to move a joint into a predetermined state, and a non-transmission mode, in which a joint can be freely moved without transmitting the driving force that has been accumulated. The control unit automatically switches the transmission mechanism to the non-transmission mode when a predetermined trigger event is recognized based on the posture of the user.
