PURPOSE: To enable to effectively operate an electric rolling stock by power drive or a brake by setting as the gate starting condition of an armature chopper the match of the direction of a field current to an operation command.

CONSTITUTION: A main circuit switch 1 is first closed or opened on the basis of the operation command P from a drive stand. A logic unit 10 starts the controlling of ON and OFF of field controllers 8-1W8-4 in response to the state signal S and the operation command P of the main circuit. A current detector 11 sets a digital amount CD1 to "1" when the field current detected by a current detector 9 is positive and a predetermined value or larger. A logic unit 12 starts the operation of ON and OFF of an armature chopper 3 after confirming that the operation command P is matched to the state signals of the digital amounts CD1, CD2. In this manner, a serious trouble of the armature circuit which occurs due the unnecessary operation of a field controller can be prevented.