To ensure given deceleration according to the travel of brake pedals despite of a change in the coefficient of friction of brake pads, prevent an overload on motor due to a reduction in the coefficient of friction, and warn the driver about the reduction in the coefficient of friction.

A gain as the function of pedal travel and motor driving current is corrected to bring actual deceleration to a given level in accordance with the pedal travel, and the motor is driven accordingly, so that given deceleration is ensured according to the pedal travel despite of a change in the coefficient of friction. The coefficient of friction is estimated on the basis of the actual deceleration and motor driving current, and a proof motor current Ia to offer proof deceleration Ga is detected. If the proof motor current Ia exceeds a maximal motor current Imax, the function expression is corrected so that the motor current Im changes below the maximal motor current Imax in accordance with the pedal travel. In this state, deceleration according to the pedal travel is no longer obtainable, which notifies the driver about the reduction in the coefficient of friction.