To unlock a key speedily and inexpensively without destructing the key.

The key information required for unlocking keys is registered into key information data base 120 in relation to the information specifying users of the keys by a key information management server 110 in accordance with demands from devices 200 installed at member stores of a chain store association. When it is demanded to output the registered key information from the device 200 installed at the member store through a network 320, the key information management server 110 retrieves the key information data base 120 based on the information specifying the user and outputs the retrieved key information to the device 200 installed at the member store. The device 200 installed at the member store displays the information on a display device 240.