To improve durability of an auxiliary brake and reduce emission of soot from an engine by optimizing a timing when the auxiliary brake actuates in a transmission control system for shortening shift time by actuating the auxiliary brake.

An engine control unit 82 sets a pseudo accelerator opening degree which gradually decreases as time passes in accordance with a shift-up command from an electronic control unit 80. The engine control unit 82 then controls an injection amount of fuel based on the pseudo accelerator opening degree. When the pseudo accelerator opening degree is smaller than a predetermined valve or the injection amount of fuel is zero, the electronic control unit 80 actuates exhaust brakes 104, 106 judging that the engine is in a no-load running state.