To make the whole unit small in size and also to reduce the power consumption by reducing the load on a motor.

A vibration generating unit 10 is provided with a prescribed vibrating force to an object of vibration 12, by making vibrating motion on the horizontal plane 12a of the object 12, and it is equipped with a return torque generating means 21, having a first torque generating means 22 and a second torque generating means 24. The first torque generating means 22 generates a "return torque" which is proportional to the number of revolutions of a wheel 18 at advancing of the unit 10 and gives this "return torque" to the wheel 18 as a propulsive force in the retreat. Meanwhile, the second torque generating means 24 generates a "return torque" proportional to the number of revolutions of the wheel 18, when the unit 10 is made to retreat and gives this "return torque" to the wheel 18 as the propulsive force in at the advancing.