Patent ID: 8368406

Claim:
An insulation measuring apparatus, comprising: a measuring circuit including a first capacitor as a flying capacitor; a control unit that is adapted to read 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 configured when one selected from a power supply voltage, a positive-electrode side ground fault resistor voltage, and a negative-electrode side ground fault resistor voltage is to be set on the first capacitor; a switching section provided in a path located between the measuring circuit and the control unit, for shutting off the path 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, wherein the control unit is adapted to control the path configuration of the measuring circuit when the control unit is to read the voltage set on the first capacitor, 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, and in the measuring circuit, a resistance value of a path that is controlled to discharge the electric charge of the first capacitor is being set to a value which the electric charge corresponding to the voltage set on the first capacitor is dischargeable in a reading period of the voltage by the control unit.