PURPOSE: To enable smooth deceleration of an engine vehicle by controlling the opening of a solenoid control valve to zero for a short period after loading or unloading is started if loading or unloading is started while the vehicle is decelerated without operating a brake pedal, and then controlling the opening of the valve to a larger one than usual for a while.

CONSTITUTION: A controller 37 determines according to the controlled variable of an accelerator pedal 7 unloading is started while the vehicle is decelerated without operating a brake pedal 31, the controller 37 controls the opening of a solenoid control valve 31 in such a manner that the opening is zero for a short period after the loading or unloading is started. The controller 37 then controls the opening of the solenoid control valve 21 in such a manner that the opening is larger than usual for a while thereafter. Therefore, even when the speed of an engine 1 is sharply increased in accordance with loading or unloading, the speed of a swash plate can be made to follow this increase and so the vehicle can be smoothly decelerated.