To provide an electronic key system having high safety allowing a wide range of use and integration.

Features of fingerprints of a person gripping an electronic key are detected and extracted, and a coded key is made based on a built-in corresponding table. A signal for unlocking created by the coded key is transmitted to a key hole side, and the code is decoded by trying all of many decoding keys based on the corresponding table built-in at the key hole side. In this way, the key can be compared with the registered information storing the features of a person decoded; when the results of comparison coincide with each other, the person is considered as a certified person and the key is unlocked.