In order to start vehicle height adjustment control even when an air suspension air tank is empty or sufficient air is not left therein, a vehicle height adjustment system includes a compressor which produces compressed air, a magnetic valve which controls air supply and discharge to/from air springs, a control unit which controls a valve opening/closing operation of the magnetic valve, an air passage which connects between the compressor and the magnetic valve through a main air tank bypassing the air suspension air tank, and an air suspension control pressure switch which detects an internal pressure value of the air passage. The control unit controls start and stop of air supply, namely, start and stop of vehicle height adjustment control at the magnetic valve, based on the internal pressure value detected by the air suspension control pressure switch.