PURPOSE: To provide a retarder control device avoiding the undesired actuation of a retarder by pedal operation other than pressure reducing braking.

CONSTITUTION: A retarder 113 for imparting pressure reducing braking to a vehicle is provided on the output side of a transmission. A control device is provided with a retarder switch 102 for putting the retarder 113 in an operable state, and the control device actuates the retarder 113 according to the pedal operation of an accelerator or the like. This control device is provided with an acceleration-deceleration sensor 112 for detecting the accelerating-decelerating state of the vehicle, and when the vehicle is detected to be in the accelerating state at the time of pedal operation, the control device inhibits the actuation of the retarder 113 by the above-mentioned pedal operation.