An insulation measuring apparatus having a measuring circuit including a first capacitor; a control unit that reads a voltage set on the first capacitor to decide an insulation state of a power supply, and control a path configuration of the measuring circuit; a switching section provided in a path located between the measuring circuit and the control unit; and a second capacitor provided between a ground and a path located between the switching section and the control unit. The control unit controls the path configuration of the measuring circuit, by turning ON the switching section to set a voltage corresponding to the voltage that is set on the first capacitor on the second capacitor, and then by turning OFF the switching section to read the voltage set on the second capacitor and to discharge an electric charge corresponding to the voltage being set on the first capacitor.