the opened state to thereby allow the brake oil to flow to the front left wheel brake 12 at the same time a current tending to flow to the exciting coil 8d for the front left release valve via a diode formed internally of the transistor 7d upon polarity reversed connection of the battery 1 is prevented by the diode 9d thus notwithstanding of the polarity reversed connection of the battery 1 the front left release valve 17d remains in the closed state as a result of which there can be avoided such situation that the brake oil flows to the front reservoir 15f from the front left wheel brake 12 to thereby release the brake pressure applied to the front left wheel brake 12 in this manner the brake application can be held effective by employing the transistors 7a to 7d each having a capacity for withstanding the reverse current they can be protected against destruction even when the battery should be connected with reversed polarity it will now be understood that in the control apparatus for the anti skid brake system according to the instant embodiment of the invention a braking force can be ensured for the motor vehicle even if the battery 1 should be connected with reverse polarity besides the control apparatus can be implemented inexpensively in a miniature size because each of the diodes 9a to 9d may be of a small capacity on the other hand no diode is inserted in any one of the drain paths of the transistors 7e to 7h.