To surely manage a key, to centrally and collectively manage key utilization states in key boxes on the remote center host side and to minimally lighten the burdens of managers for each key box.

A lending key in a type that a key can be detached from a key cylinder in case of locking but the key is held to the key cylinder in the case of unlocking is used. A large number of the key cylinders 11 and selector switches 24 are disposed on the front panel surface 22 of the key box 20, key detecting control mechanisms 30 detecting the presence of the installation of the key while permitting and controlling the rotation of the key are incorporated at every key cylinder in the key box, and a card reader section 32 reading the data of use cards is mounted. The turn-on of the selector switches is permitted to adequate use and the corresponding key can be lent, and the key is returned by fitting to the key cylinders of the key.