The purpose of the present invention is to provide a component that promotes the growth of leguminous plants. Provided are: a promoter for leguminous plant growth, which contains a glycoside of Soyasapogenol B as an effective component; and a method for promoting the growth of leguminous plants using a glycoside of Soyasapogenol B as an effective component. The glycoside of Soyasapogenol B has a hydroxy group at position C-22 of Soyasapogenol B, and the hydroxy group at position C-3 of the Soyasapogenol B has a sugar bonded thereto.