We investigated the influence of the placement and amount of the applied calcium superphosphate on the early growth of direct-sown onions (Allium cepa L.) on Andosols. The effect of localized fertilizer application was compared with broadcast application. The placement of calcium superphosphate below the onion seed may affect the early growth of onions, especially in the early growth stage. Fertilizer placed 0 to 4 cm below the seed was more effective than broadcast application. Seedling emergence based on the amount of calcium superphosphate 0 cm below the seed was not affected by the amount of calcium superphosphate in our experiment. The soil solution EC value of localized calcium superphosphate did not affect seedling emergence. These results suggest that the most effective placement of phosphatic fertilizer is directly below the seeds, and the effective amount to be applied is 30 or 45 kg・10 a⁻¹ as P₂O₅.