PURPOSE: To supply empty case to the standby part without using human labor by transferring cases, which are loaded with sheets of paper in standby at the standby part to a transport means, and transferring empty case transported by this means to the standby part in unloaded condition.

CONSTITUTION: When carrying-out of a case 21 loaded with mail has been done, a stopper 33 for supply of empty case shall be released. This supplies an empty case 21 to main conveyors 11, 11 from the empty case supply part 32. Immediately before this empty case supplied 21 reaches an appropriate transfer unit 16, it shall be put in contact with a stopper 19 of that transfer unit 16, which is situated downstream the named transfer unit 16, and be stopped on its conveyors 18, 18. Then the first named transfer unit 16 is lifted, and conveyors 14, 14, 18, 18 are operated in the direction moving apart from the main conveyors 11, 11 as opposite to the time when the case is carried out, and the empty case 21 is sent toward the applicable standby unit 13.