A power assist device includes: holder holding a workpiece; a pair of wires each having one end connected to the holder to suspend the holder; a pair of wind-up wheels winding up respective other ends of the wires; a pair of motors rotationally driving the respective wind-up wheels; a pair of rotation detectors detecting rotation information of the respective motors; a pair of torque detectors detecting drive torque in the respective motors; and controller controlling drive of the motors. The controller calculates operating force to the workpiece based on the rotation information detected by the rotation detectors and the drive torque of the motors detected by the torque detectors, and controls the motors to assist the operating force that is calculated, to move up and down the holder.