To provide a key having the certification-opening/closing function of the unlocking without inserting the key to achieve the unlocking.

An IC card 3 transmits the user identification information recorded in a memory 34 to a certification-opening/closing function unit 1. The certification-opening/closing function unit 1 receives the user identification information, and then, transmits it to a collation unit 15 by a control unit 11. The collation unit 15 collates the user identification information transmitted from the IC card 3 with the user identification information recorded in a memory 16. The collation unit 15 judges that the user is identified when both user identification information agrees with each other, and transmits the collation signal to the control unit 11. The control unit 11 receives the collation signal, and gives an instruction of opening the key of a door 2 to an opening/closing control unit 17. The opening/closing control unit 17 opens the key according to the instruction from the control part 11.