PURPOSE:To obtain a correct real value of current supplied to an air conditioner by inputting current waveform in digital data and obtaining an average of the digital data. CONSTITUTION:Voltage at an output terminal (a) of a current transformer 33 is applied to an A/D port of a microcomputer 41, which takes in this data at an interval of 500musec. Voltage of +5V is applied to a series circuit formed of voltage divider resistor 92a and 92b. At this time, the divider resistors 92a and 92b having the same resistance value, a connection point of the resistors 92a and 92b, that is, an output terminal (b) of a current transformer 33 is at +2.5V. A resistance value of a resistor 91 is set at such a value as a voltage variation at the output terminal (a) of the current transformer 33 can go up and down by 2.5 with respect to +2.5V (the voltage at the output terminal (b)), and at the same time, as a peak value of the current correspond to 30V in the case that the voltage is 2.5V on positive side.