PURPOSE: To increase the function of the engine brake by applying load, during brake operation, to the hydraulic pump driven, as an integral part, by the main shaft of vehicular motor.

CONSTITUTION: When the vehicle is decelerated, the switch valve 8 is switched to the position by interlocking with the brake pedal 7 and hydraulic oil fed from the hydraulic pump 2 is supplied directly to the relief valve 10. Hydraulic oil fed to the relief valve 10, when pressurized up to the set pressure, overflows and returns to the tank through the pipe passage 11. When this hydraulic oil is pressurized up to the set pressure of the relief valve 10, load is applied to the hydraulic pump 2. This load decreases the rotation of the main shaft 3 of the vehicular motor which is connected, as an integral part, to the hydraulic pump 2. This function serves as auxiliary engine braking function, contributing to reducing vehicular speed.