PURPOSE: To provide a simplified constitution with a less number of parts by providing a first input terminal which is in contact with one end of a voltage source and a second input terminal which is in contact with one end of the voltage source preceding the first input terminal.

CONSTITUTION: When one end of a power supply board 31 is inserted into a connector 23, a second input terminal 34 and a third input terminal 35 located outside the power supply board 31 than a first input terminal 33 are in contact with a second voltage supply terminal 25 and a third voltage supply terminal 26 of the connector 23. In this stage, a surge current into a capacitor 37 from a voltage source 22 is controlled by a surge current limiter resistor 39. Thereafter, when one end of the power supply board 31 is further inserted into the connector 23, the first input terminal 33 is also in contact with the voltage supply terminal and therefore an input voltage from the voltage source 22 is supplied in direct to an inverter 32 without consumption in the surge current limiter resistor 39.