PURPOSE: To use one exciting circuit in common for current driving and voltage driving, by connecting voltage driving rectifier to a circuit comprising a diode bridge, a reference voltage signal generating circuit, an amplifier, and an active element, through circuit switching elements.

CONSTITUTION: When only a switch J3 of switches J1WJ7 is turned OFF, a current driving type exciting circuit is formed, and an exciting coil L is driven by the current through terminals Ix1 and Ix2. In the meantime, when only the circuit switch J3 is turned ON, capacitors C1 and C2, a diode D2 for protecting a reverse voltage, and a current limiting element Q2 are excluded from the circuit constitution, and the voltage driving rectifier 2 is incorporated into the circuit. Thus a voltage driving type exciting circuit is formed. Then the exciting coil L is driven by the voltage through output terminals Ex1 and Ex2 of the rectifier 2.