PURPOSE: To carry out automatic regulation so as to match real rotational speed of each mode such as idling, light excavation, standard excavation, and heavy excavation, with the target rotational speed of each mode.

CONSTITUTION: A throttle motor 1 for rotating an engine governor lever 14 is driven by a signal from an interface 3 though a driver 2, and the interface is connected to a CPU 6 for comparatively calculating a target engine rotational speed with a real engine rotational speed. In the CPU 6, a non-volatile ROM 7 for maintaining a read-in data and an A/D converter 8 for converting voltage into a digital value are connected independently, and also a sensor for detecting the real engine rotational speed and an integrated circuit 9 for converting the frequency signal from the sensor 11 into voltage and transmitting a voltage signal to the A/D converter 8 are provided, furthermore, a feed back circuit 12 for transferring a same signal as a signal transferred from a driver to the throttle motor 1 is provided between the driver 2 and the CPU 6 so as to enable automatic regulation.