A precursor solution of a garnet-type solid electrolyte is provided that is represented by the following compositional formula, and contains one type of solvent, and a lithium compound, a lanthanum compound, a zirconium compound, a gallium compound, and a neodymium compound, each of which has solubility in the solvent, wherein with respect to the stoichiometric composition of the following compositional formula, the amount of the lithium compound is 1.05 times or more and 1.30 times or less, and the amounts of the lanthanum compound, the zirconium compound, the gallium compound, and the neodymium compound are equal, (Li7−3xGax)(La3−yNdy)Zr2O12 provided that the following relationships are satisfied: 0.1≤x≤1.0 and 0.0