PURPOSE: To control vibration due to shape of road surface effectively by providing pressure adjusting means on both enclosed volume parts in an air cylinder, and enclosing a flow rate adjusting means with an air pressure circuit shortcircuiting both enclosed volume parts.

CONSTITUTION: An air cylinder 1 and a spring 40 are equipped between a vehicle body 30 and a shaft 31, and a piston rod 3 of a piston 2 to the shaft 31, and the end part of the cylinder 1 to the vehicle body 30 are connected to each other. Pressure adjusting means 4, 5 controlling the pressures as corresponding to the needs for enclosed volume parts 1a, 1b in the cylinder 1 are respectively provided side by side, and a first air pressure circuit 11c short-circuiting both enclosed volume parts 1a, 1b to each other is provided and a flow rate adjusting means 6 is enclosed in the middle thereof. Effective shock absorbability is performed for individual shock acting the axle shaft 31 owing to the shape of the road surface. If a compressor 10 should break down, it is possible to fulfil the suspension on function thoroughly by closing suspension controlling electromagnetic valves 4, 5.