A hydraulic cylinder extends to cause a second hook to slide away from a first hook. The hydraulic cylinder contracts to cause the second hook to slide towards the first hook. A connecting pin connects a first end part of the hydraulic cylinder to a main coupler body. The main coupler body has a support hole. The support hole moveably supports the connecting pin in the direction of extension of the hydraulic cylinder. The first end part of the hydraulic cylinder moves away from a second end part within the movability range of the connecting pin and thereby moves a lock member from a lock-OFF position to a lock-ON position.
