PURPOSE: To switch a speed control to a current control or vice versa shocklessly by eliminating the abrupt change in the command input of a current regulator immediately before and after switching when switching the command input of the regulator.

CONSTITUTION: A subtracting circuit 1 has a subtractor 11 and a polarity inverter 12 to form Y-X, X-Y from the output X of a speed regulator 7 and the output Y of a current command generator 6 and to input them to switches 21, 22. The switch 21 opens or closes the output Y-X of the subtractor 11, and the switch 22 opens or closes the output X=Y of the inverter 12. Calculators 31, 32 delay the outputs Y-X, X-Y to attenuate them. An adder 41 adds the signal X to the output Y-X of the calculator 31. An adder 42 adds the signal Y to the output X-Y of the calculator 32. A selector 5 selects either one of the adders 41, 42 and outputs the input Z of the regulator 8.