An ingredient for promoting the growth of legumes is provided. A leguminous plant growth promoter comprising soyasaponin and HLB 9-20 nonionic surfactant as active ingredients. [Selection diagram] None【課題】マメ科植物の生育を促進する成分の提供。【解決手段】ソヤサポニンおよびHLB9~20の非イオン性界面活性剤を有効成分とする、マメ科植物生育促進剤。【選択図】なし