PURPOSE: To ensure the drainage of seedling boxes from the seedling box cleaner so that the boxes are treated with a disinfectant solution and the solution can be drained when the boxes are sent out of the cleaner.

CONSTITUTION: The drainage and disinfection unit (B) are set on the outlet side of the seedling box cleaner (A) and the unit is divided with a plate 3 into the draining chamber C and the disinfectant solution chamber D. The draining chamber (C) is provided with a drain-receiving conduit 23 at the bottom toward the outlet 22a of the cleaner (A), while the disinfectant solution chamber (D) is equipped with another conduit 25 at the bottom for sending the solution to the solution tank 31 so that the reuse of the solution is made possible.