An electronic key apparatus for vehicle includes a vehicle mounted device, and a portable device. The vehicle mounted device operates a controller upon authenticating an ID code of the portable device by communication with the portable device, and includes a first sending/receiving unit, a first memory that stores ID codes to authenticate portable devices, a first CPU that sends a request signal to the portable device, and receives and decodes whether an answer signal matches the ID code, and a driving unit that outputs a control signal. The portable devices includes a second sending/receiving unit, a second memory that stores a unique ID code, and a second CPU that encrypts the unique ID code and sends an answer signal. The vehicle mounted device includes a disablement unit that temporarily suspends use of an ID code, and does not communicate with the portable device with the suspended ID code.