To provide a lock monitoring device effective in preventing, without using a key having a special structure, burglar such as picking by emitting an alarm upon detecting unlocking carried out by a process different from a predetermined process.

In the lock monitoring device, an unlocking starting signal which is a starting point of unlocking operation is emitted by operating a button arranged secretly at a predetermined place. When an unlocking signal is received within a predetermined time after receiving the unlocking starting signal, the device is determined to be in normal operation. When the unlocking starting signal is not received before the unlocking signal is received, an alarm signal is emitted immediately. When the unlocking signal is not received even after a predetermined time set as a time for unlocking by a legitimate key elapses from a time of receiving the unlocking starting signal, the alarm signal is emitted at the time of elapsing the predetermined time.