To improve braking responsiveness of a service brake without damaging an auxiliary braking mechanism even in a braking device having an auxiliary braking mechanism.

This brake device circuit includes a brake valve 4 for regulating the pressure of air from an air tank 5 to braking signal pressure according to an actuating amount of a brake pedal 6, relay valves 11, 12 disposed on the downstream thereof for regulating the pressure of air from the air tank to the braking output pressure, a first supply line r1 formed by providing a first one-way route c1 of a double check valve 21 in the midway between an outline 14a of the relay valve 12 and a wheel cylinder 3 provided corresponding to wheels, valve devices 23, 24 for regulating the pressure of air from the air tank 5 to the auxiliary braking output pressure according to an auxiliary braking signal output by an auxiliary braking control device 49, and a second supply line for connecting the valve device 23, 24 to the wheel cylinder 3 through a second one-way route c1 of the double check valve 21.