PURPOSE: To provide a brake pressure operating device without technical additional cost as a brake pressure control valve of a driving wheel comes to be at a blocking position when one of the driving wheels has a slipping tendency and a motion control valve removes pressure of a control pressure space.

CONSTITUTION: A brake pressure setting device 10 is furnished with a fastening preventive device and a driving slip control device and is provided for control of brake pressure decreasing, holding and reforming stages of fastening preventive control and for control of brake pressure forming, holding and brake pressure reforming stages of driving slip control. Consequently, when a slipping tendency of a left side rear wheel increases and exceeds at least one of upper side limit values of both of driving slip of the wheel or acceleration for the wheel, a brake pressure control valve 56 is returned to a basic position, a pressure modulator 21 moves to decrease capacity of a modulating chamber 34, a wheel brake 11 is pushed into a wheel brake cylinder, and this wheel is braked.