PURPOSE: To remove a defective seedling and enable transplanting of only grad ed seedlings of good quality even if the defective seedling is held by part of seedling holding units.

CONSTITUTION: In an automatic seedling feeder of a transplanter in which seedling holding units 63 of each feeding mechanism 57 are successively transferred to a dropping position (A) and each of the seedlings held by each seedling holding unit 63 is successively dropped from the seedling holding unit 63 at the dropping position (A) to a transplanting part, a defectiveness sensor 97 for sensing that the seedling in the seedling holding unit is bad is installed and a drop preventing mechanism for preventing the defective seedling sensed by the aforementioned sensor 97 from dropping from the seedling holding unit to the transplanting part is further provided. Furthermore, the above-mentioned feeding mechanism is intermittently driven at a high speed after sensing with defectiveness sensor 97 and then intermittently driven at 2 pitches so as not to stop the seedling holding unit holding the defective seedling from stopping at the position for dropping.