In PID control of engine speed, an I component is used as an integral control value by integration of speed difference between a target engine speed and an actual engine speed. In this case, when the actual engine speed is lower than the target engine speed, the integral control value of the I component is integrated continuously and increased, thereby leading an evil influence that the integral control value becomes too large.
The Patent Literature 1 discloses an electronic governor in which an integrated value is calculated based on reduction rate of the target engine speed, the speed difference between the target engine speed and the actual engine speed and the like, and a value stored previously and less than the calculated integrated value is set as the integral control value, whereby response time can be shortened in the case that the actual engine speed is reduced from high speed state to low speed state.
However, in the electronic governor disclosed in the Patent Literature 1, for example in the case that a traveling vehicle finishes traveling with actuating an engine brake, that is, in the case that the actual engine speed has been more than the target engine speed continuously by an external factor such as a downward slope and then the external factor is canceled and the actual engine speed converges on the target engine speed, it is disadvantageous that the reduction amount of the actual engine speed about the target engine speed cannot be suppressed.    Patent Literature 1: the Japanese Patent Laid Open Gazette 2006-274881