PURPOSE: To make detectable normally operating a solenoid valve or the like in a condition particularly that an oil pressure is applied, by generating a simulated slip signal when detected respectively a step-in of a brake pedal, parking condition of a transmission and a zero speed.

CONSTITUTION: Stepping in a brake pedal 12 is detected by a brake sensor 14, and placing a transmission in a parking condition is detected by a shift position sensor 16, further to detect a speed zero by a wheel speed sensor 18. By these detections, a simulated slip signal is generated from a simulated slip signal generating means 20, to perform antilock brake control in accordance with this simulated slip signal. In this way, since the antilock brake control can be performed, a trouble of solenoid valve or the like in a condition with an actual oil pressure applied can be accurately detected.