To securely prevent a user from forgetting to lock up.

A key holder 1 comprises a thyristor circuit, a battery, an LED, a vibration motor accommodation chamber, and a back cover 6. In the accommodation chamber, a switch and a cut switch rod are also installed. The key holder 1 is constituted by sandwiching a key 2 between the accommodation chamber and the back cover. They are always set like this, and inserted into a key holder head 7 at home. When the user goes out, the key holder is drawn out downward, and then the switch operates to start light emission by the LED and vibration. The key should be inserted into the lock of a door so as to stop them. A putting-back alarm lamp 12 of the LED continues to illuminate on the key holder head so as to urge the key holder to be put back into the key holder head. Once the key holder is inserted into the key holder head, the alarm goes off.