A voltage detector detects a voltage of a positive electrode of a battery, and outputs a detection value indicating a detected voltage value. A target voltage to be detected is applied to one end of a resistor, via a first switch. A current is input to an output circuit from the other end of the resistor. The output circuit outputs a current whose current value substantively coincides with the current value of the current input from the resistor to one end of a resistor, while maintaining a voltage value of the other end of the resistor substantively at a predetermined voltage value. A voltage value of the one end of the resistor is output to a microcomputer as the detection value.