An improved anti-lock brake device of simple and compact construction adapted for use with a motorcycle having front and rear master cylinders for actuating front and rear wheel brakes, respectively. The front master cylinder has a first brake chamber for producing a brake torque for a front road wheel and a first control chamber for controlling the brake torque so as to prevent locking of the front wheel. The rear master cylinder has a second brake chamber for producing a brake torque for a rear road wheel and a second control chamber for controlling the brake torque so as to prevent locking of the rear wheel. The control chambers are each in communication with a single common source of oil pressure through a first control valve and with an oil tank through a second control valve.