PURPOSE: To secure safety in a manner such that returning of an accelerator does not generate a power running but regeneration or coasting is performed by a method wherein the switching of a chopper into a power running mode is performed by the AND of a power running change-over signal from a microcomputer and an accelerated switch signal.

CONSTITUTION: Switch signals of an accelerator 1, key switch signals of a key switch 3, chopper current signals and field current signals are entered in an I/O circuit 7, and using an operation patterns stored in a memory 9 consisting of RAM and ROM, an operation of optimum chopper flow rate and discrimination for switching of chopper on a power running and a regeneration mode are performed by means of a MPU8, thus, a power running switching signal is sent from the I/O circuit 7 and further, choppers 23W27 are changed-over to a power running mode by the AND of the power running switching signal sent from the I/O circuit 7 and the accelerator signal from the accelerator 1. At this time, when an accelerator is returned, a power running is not always performed, as a result, even when a microcomputer consisting of the I/O circuit, MPU and a memory performs a mulfunction, unexpected run can be prevented.