A secondary battery according to the present disclosure includes a solid electrolyte portion containing a lithium composite metal oxide represented by the following compositional formula (1), and current collectors disposed opposite to each other through the solid electrolyte portion: Li7−xLa3Zr2−(x+y)MaxMbyO12  (1) provided that 0.5 8 wherein i is an oxidation number of Ma and j is an oxidation number of Mb are satisfied, and Ma represents one or more types of Sb, Bi, Ce, Mn, V, Te, Tc, and Sn, and Mb represents one or more types of Nb, Cr, Mo, W, Ta, and Ti.