To stably provide a grounded load necessary for preventing the tilt of a car body by each outrigger mechanism in a vehicle vibration preventing device having a plurality of outrigger mechanisms.

When a transfer starting signal Ss is inputted to a control section from the outside, the control section outputs a forward rotation command to each motor 3a of an outrigger mechanism and thus each motor 3a is rotated forward and each rod 10 is moved in the road surface direction. When a stopper 12 is grounded to the road surface and the motor 3a continues to be rotated, a grounded load is gradually increased and when detecting signals are outputted from all the grounding force detecting circuits 11 of the outrigger mechanisms, the control section 30 outputs a rotation stopping command and a braking command to each motor 3a and each brake 3b and thereby all the motors 3a are simultaneously stopped and all the brakes 3b are actuated and these conditions are maintained.