PROBLEM TO BE SOLVED: To directly load pot seedling boxes on a seedling transplanter without requiring much labor for taking out the pot seedling box from a seedling box- carrying cage and automatically feed the pot seedling box to a seedling-placing table. SOLUTION: This method for automatically feeding the pot seedling boxes comprises housing these pot seedling boxes into a seedling box-carrying cage 1 composed of a nearly rectangle opening frame through which the pot seedling box P is loaded or unloaded, a plurality of vertical frames for placing pot seedling boxes in parallel and bottom frames with which one ends of these pot seedling boxes are brought into contact and directly setting the seedling box-carrying cage 1 to a lifting and lowering base 29 of an automatic feeder 16, lowering the lifting and lowering base 29 by every interval of the vertical frame, taking out the pot seedling box from above the vertical frame whenever the lifting and lowering base 29 stops and sending out the pot seedling box to a seedling box-introducing part 20 of a planting device 15.
