To perform a motion similar to pendulum motion by connecting the rocking elements of rocking generating devices provided on the upper ends of both lateral leg parts to a seat part, and moving the seat part from the horizontal direction to the forward upper direction.

A rocking element 2 is formed of at least, two rotating bodies 3 fixed by a rotating body fixture 4 and a connecting plate 5 with a seat part fixed to the rotating body fixture 4. A rocking generating device 1 has the rocking element 2 integrated into a rocking element receiving base 6 having a rotating body guide elliptic hole 12. This device is set on the upper ends of both lateral leg parts 8, and the respective side surface parts of each rocking element 2 and the seat part 9 are connected by the connecting plate 5 with the seat part. The front end parts of armrest parts 10 are held by both hands, and pulled to this side so if the oars of a boat are pulled, whereby the seat part 9 situated in substantially horizontal state is moved in forward upper direction, and laid in backward tilted state. When the pulling force of both the hands pulled to this side is loosened, the seat part 9 moved in the forward upper direction is returned substantially to the horizontal state. This operation is repeated with good timing, whereby the seat 9 can continue a rhythmical rocking.