To provide a locking device capable of maintaining a lock pin in a constantly normal posture and adequately locking and unlocking a working body.

In the locking device, a working body 30 moving between the locking position and the unlocking position in a housing 22 has a lock cam (a heart cam 32), and when the working body 30 is moved to the locking position, a fore end of a lock pin 70 is located at a locking unit of the lock cam to hold the working body 30 at the locking position. An elastic plate 60 is assembled between the housing 22 and a cap 50 to be covered over its opening part. The elastic plate 60 is deflected to demonstrate the elastic force to at least one inner surface of the housing 22 and the cap 50, and a supporting unit formed on a base end of the lock pin 70 is held and supported between the elastic plate 60 and the cap 50.