A hydraulic power unit (5) mounts integrally an electronic unit (6) in an antilock brake system. The unit (5) has a solenoid tab (5ab) containing a coupling pin connected to a coil of a solenoid valve (5a). The electronic unit (6) has a connector for a power source, a motor relay (7), terminal sections (61Ba, 61Bd, and 61Be) for fail-safe relays. The coil in the solenoid valve (5a) is electrically coupled to an electronic control section, and the terminal sections (61Bd and 61Be) in the electronic unit (6) by coupling the solenoid tab 5ba to a solenoid socket (14) in the electronic unit (6). This construction makes it easy to electrically interconnect the coil of the solenoid valve in the hydraulic power unit (5) and the electronic unit (6).