The present invention provides a pusher dog, which is mounted on a driving conveyor chain and normally urged to a standing position, and which is detachably hooked on a truck. The pusher dog tilt operation plate is mounted on a storage conveyor. An upward urging member pushes up the pusher dog tilt operation plate to abut a lower end portion of the pusher dog in such a direction that the pusher dog is made to tilt and is released from engagement with the truck. A press down member presses down the pusher dog tilt operation plate against the upward urging force.
