Key holding device for in-vehicle auxiliary key

An electronic key system for operating a vehicle, comprising:

• a master key, an auxiliary key, and an in-vehicle key holding device for said auxiliary key, the key holding device comprising:
• a key cylinder capable of retaining the auxiliary key which is a vehicle key that is not a master key;
• a rotor rotatably arranged in the key cylinder, in which the auxiliary key is insertable into the rotor;
• a tumbler rotatable with the rotor in the key cylinder, in which the tumbler holds the auxiliary key in a manner irremovable from the key cylinder in accordance with the rotational position of the rotor;
• a key lock mechanism capable of locking the rotor in a state in which the tumbler holds the auxiliary key in a manner irremovable from the key cylinder;
• a control unit for switching the rotor between a locked state and an unlocked state by controlling the key lock mechanism so as to permit removal of the auxiliary key when the rotor is in the unlocked state;
• and
• a restriction setting unit that controls whether vehicle functions are usable with the auxiliary key in accordance with a selection of a user, wherein the vehicle functions are usable with the master key, but not all of the vehicle functions are usable with the auxiliary key.