A proportioning valve assembly employs an electromagnetic acuator, such as a proportioning solenoid, associated with a driver circuit. The driver circuit is provided a lead phase circuit for providing a lead phase in supplying a supply current for controlling the valve position of the proportioning valve. Providing appropriate lead time reduces necessity of high gain in attitude change suppression mode operation. Therefore, the response characteristics in pressure adjustment in the shock absorbing mode operation, can be prevented from falling an excessive level.