To perform trouble-free operations for connecting/releasing the bogie of a yard truck and the like.

This device is provided with a hook 15 which is so supported by a driving bogie 1 that it can be locked on/released from its ring 12 where the driven bogie of a yard truck is provided with the ring 12, a manual lever 24 permitting the hook 15 to be released from the ring 14 when both the bogies are released from each other, locking members 27 and 28 locking the hook 15 onto its releasing position, and with an operation member 29 which releases the lock of the hook 15 locked by the locking members 27 and 28 upon receiving a signal given by the abutment of the ring 12 when both the bogies are connected with each other. The hook 15 is rotatably supported by the base end side in such a way that it can be energized to the locking direction by its dead weight, and its rotatably supporting position is provided for a place down below the tip end position at the locking side of the hook 15. A retaining part 15a is provided, which is inclined to the locking side of the hook 15.