The present invention provides a motion assist apparatus capable of reducing the discomfort of a user that may be caused when a motion is assisted. A motion assist apparatus 1 has actuators 11, which apply a force for controlling the posture of the upper body of a user P through the intermediary of a second frame 14, a posture estimation sensor PS, which detects a posture angle &thetas of the upper body of the user P, a control unit C, which controls the actuators 11 to reduce a deviation d&thetas of a posture angle &thetas from a reference posture angle &thetas0, and a trigger sensor TS, which detects the occurrence of a trigger event. The control unit C sets the posture angle at the time of the occurrence of the trigger event as the reference posture angle &thetas0.
