To prevent a fraudulent action from being conducted by disassembling a lock device.

The lock device 1 includes: a lock device main body 10; loop-like circuit parts 23, 26, 29 and 32 for electrically connecting an outer side escutcheon 13, a cylinder unit 14, an inner side escutcheon 16 and a thumb-turn unit 17 respectively; detection parts 21, 24, 27 and 30 for detecting the disconnections of the loop-like circuit parts 23, 26, 29 and 32 respectively; and a control part 33 and a buzzer 34, etc., for outputting buzzer sound when the respective detection parts 21, 24, 27 and 30 detect the disconnections of the respective loop-like circuit parts 23, 26, 29 and 32. When one of the outer side escutcheon 13, the cylinder unit 14, the inner side escutcheon 16 and the thumb-turn unit 17 is detached from the lock device main body 10 or a door 2, the buzzer sound is outputted.