To provide a rotating operation support structure of a mechanical key provided to an electronic key, which can support the rotating operation of the mechanical key and can miniaturize the electronic key even if the structure has such a support mechanism.

The mechanical key 40 is detachably stored in the electronic key which wirelessly transmits an ID code to a vehicle so that the vehicle can collate the ID code, and under the condition that the collation of the ID code is established, enables the devices mounted on the vehicle to be operated, and in which the collation of the ID code is performed by an actual mechanical operation. The rotating operation support structure of the mechanical key 40 includes a rotating operation support mechanism 3 for supporting the rotating operation by removing the cylinder cover 53 of a key cylinder 51 to which the mechanical key 40 is inserted from the vehicle and mounting the cylinder cover 53 on the mechanical key 40 for use as a holding part so that a force can be easily applied to the mechanical key 40 when the mechanical key 40 is inserted into the key cylinder 51 for rotation.