A solid-state electrolyte having a garnet-type crystal structure represented by the formula (Li7−ax+yAx)La3(Zr2−yBy)O12, where A is at least one element selected from Mg, Zn, Al, Ga, and Sc, a is a valence of A, B is at least one element selected from Al, Ga, Sc, Yb, Dy, and Y, x is more than 0 and less than 1.0, y is more than 0 and less than 1.0, and 7−ax+y is more than 5.5 and less than 7.0).