A swinging drive device (12) installed on a base (11) comprises a crank member (22a), a rod member (22b) and a link member (23) for converting both of the alternating forward and reverse rotations and the unidirectional rotation of a motor (20) into the swinging motion of a body support member (13). A controller (24) rotates the motor (20) in one direction when the body support member (13) is swung with the maximum amplitude.