To prevent a power reception unit from having trouble due to a DC voltage supplied from a power supply unit.

An AC adaptor 20 controls a transistor 42 to be turned on and off in a state where a main switch 40 is turned off, i.e. the supply of a predetermined DC voltage to a printer body 50 is limited, thereby outputting an authentication start command to the printer body 50 via a voltage feeding line 36. In this case, the DC voltage is stepped down by a resistor 38 serially connected to the voltage feeding line 36 and is supplied to the printer body 50. After that, an authentication response signal is input from the printer body 50 via a terminal P2, and the main switch 40 is turned on when the printer body 50 is authenticated based on the authentication response signal. Thus, the voltage feeding line 36 supplies a predetermined DC voltage to the printer body 50 without intervention of the resistor 38.