Abstract: A device for reciprocating a bed or cradle on supporting rods has a driving pulley (1) on a rotational first axle (50) of a driving motor (M) and a first decelerating pulley (2) on a second axle (23). The first decelerating pulley is connected to the driving pulley (1) by a first belt (7A). A first small pulley (3) on the second axle (9A) is connected to a second decelerating pulley (4) on a third axle (9B) by a second belt (7B). A second small pulley (5) on the third axle (9B) is connected to a third decelerating pulley (6) on a driving axle (8) by a third belt (7C). A disk (11) axially on the driving axle (8) has an eccentric axle (12) thereon. An idle cap (13) on the eccentric axle (12) for rotation has springs (14 and 14a) on opposite sides thereof. Supporting rods (16) are respectively connected to the springs (14 and 14a) for being moved back and forth or from side to side by tension of the springs (14 and 14a) as the rotational disk (11) is rotating.