The invention relates to a brake system for a mobile working device, for example a logging machine or a tractor backhoe loader. Said mobile working device is provided with two power brake valves (10, 16) for actuating the brakes and which are actuated by the driver according to the orientation in the cockpit for example when driving on a road and when the driver looks behind. According to the invention, a tank connection adapter (T) of a power brake valve (10) is connected to the brake connection (BR) of the second power brake valve (16), so that the first power brake valve (10) is connected to the hydraulic fluid tank by means of the tank connection adapter (T) of the second power brake valve (16) and during the actuation of the second power brake valve (16), the brake pressure thus arising is injected into the first power brake valve (10) via the tank connection adapter (T) of the first power brake valve (10), so that the brake connections (BR1, BR2) thereof are correspondingly impinged upon by the brake pressure.