To provide a control mechanism for an engine on a work vehicle for deceleration in relation to set rotation speed, intermediate position rotation speed, and idling rotation speed, in which fuel injection control is included for reducing black smoke in returning to originally set rotation speed.

In a work vehicle loading the engine provided with an electronic governor mechanism G, a deceleration switch 5 installed on a work machine lever is pushed to instantaneously change engine rotation speed from the set rotation speed to the intermediate position rotation speed, the idling rotation speed, or the originally set rotation speed. In restoring the originally set rotation speed, fuel injection quantity is controlled for reducing black smoke.