To stack seedling culture boxes with high alignment accuracy in a seedling culture box stacking mechanism for stacking and locking the seedling culture boxes sequentially from below.

This seedling culture box stacking mechanism is provided with lift members 18 for lifting the seedling culture boxes w in a scoop-up manner, and elastically retreative locking claws 24 for stopping and locking the lifted seedling culture box w from both lateral side lower parts. The seedling culture box stacking mechanism is constituted to stack and lock the supplied seedling culture boxes w sequentially from below. A box lifting operation part of the lift member 18 is composed of a freely idling rotation body 21 to allow the lifted seedling culture box w to laterally roll, and the back face s1 on the seedling culture box lifting passage side of the locking claw 24 is formed as an inward inclined face.