PURPOSE: To prevent influence to rotational control by bias current of a reference voltage source, by a method wherein a buffer circuit is installed between a resistor installed corresponding to internal resistance of a DC motor and the reference voltage source.

CONSTITUTION: In an electronic governor, a DC motor 6, a transistor 8 and a resistor 10 are connected in series between a power source terminal 2 and a ground side terminal 4, and a resistor 12 corresponding to internal resistance of the DC motor 6, a transistor 14 and a resistor 16 are connected in series. A comparator 20 supplies current corresponding to difference voltage between definite reference voltage Vref generated in a reference voltage source 24 and back electromotive force generated in the DC motor 6 to the bases of the transistors 8 and 14. Then a buffer circuit 26 is installed between the resistor 12 and the reference voltage source 24. In this constitution, current flowing through the resistor 12 and definite current to the reference voltage source 24 can be separated, and influence to the current flowing through the resistor 12 can be avoided.