Vehicular electronic key system

A vehicular electronic key system comprising:

• a vehicle having a key cylinder;
• and
• a portable device comprising:
• a key body that is communicatable with the vehicle;
• a mechanical key that is attachable to and detachable from the key body and that mechanically rotates the key cylinder whereby the communication between the vehicle and the portable device allows the vehicle to execute predetermined functions;
• and
• the key body including a key detector configured to detect an attachment state and a detachment state of the mechanical key to and from the key body so that the key body transitions to a valet mode to limit some of the predetermined functions executable by the vehicle in accordance with the communication between the vehicle and the portable device while the key detector detects the detachment state of the mechanical key from the key body, wherein
• the mechanical key includes a transponder which is supplied with power from the vehicle to send a unique signal,
• the vehicle includes a vehicle-side transponder communication device which supplies power to the transponder of the mechanical key to carry out communication with the vehicle-side transponder communication device, and an engine start device capable of starting an engine of the vehicle through the communication of the vehicle-side transponder communication device with the transponder, and
• the key body includes a key-side transponder communication device which communicates with the transponder and outputs a communication result with the mechanical key attached to the key body,
• whereby the key detector detects the attachment state and the detachment state of the mechanical key to and from the key body based on the communication result output from the key-side transponder communication device.