A hydraulic modulator including a motor having a motor housing, a stator, a rotor, and a motor shaft. A power transmitting mechanism is provided for transmitting the power of the motor to the outside thereof. A master cylinder includes a piston linearly movable by the power transmitted by the power transmitting mechanism. The master cylinder is arranged so as to overlap the motor housing in such a manner that the axis of the master cylinder is substantially perpendicular to the axis of the motor shaft. The master cylinder is arranged on one side of the motor housing in the range corresponding to the axial length of the motor shaft. The length of the hydraulic modulator along the motor shaft falls within the axial length of the motor shaft, so that the hydraulic modulator can be reduced in size.