To provide a fingerprint collating locking/unlocking device which facilitates mounting thereof on an existing door while allowing an existing lock mechanism to remain as it is.

When the door 23 is locked from inside, a locking button 14 of a control unit 10 is pressed, and when the door is unlocked, an unlocking button 15 is pressed. Then a power source of a built-in battery is automatically switched on, and the control unit 10 activates a driving section of a deadlock unit 16 in a normal or inverted direction, followed by advancing a deadlock 19 into a strike 45 or retreating the former from the latter, to thereby lock/unlock the door 23. When the door 23 is locked from outside, a cover 3 of a fingerprint collating unit 1 is opened, and a power source switch 8 arranged on a front surface of a unit main body is pressed to switch on a power source of the control unit 10, followed by operating a predetermined pressing switch 7, whereby the control unit 10 activates the deadlock 19 of the deadlock unit 16 and carries out locking. When the door is unlocked, the power source switch 8 is pressed to switch on the power source, and a fingerprint is read by the fingerprint collating device 5. If the fingerprint of the control unit 10 coincides with a registered fingerprint, the door is unlocked.