A positive-electrode body 1 is prepared that includes a positive-electrode active-material layer 12 including a powder-molded body, and a positive-electrode-side solid-electrolyte layer (PSE layer) 13 that is amorphous and formed on the positive-electrode active-material layer 12 by a vapor-phase process. A negative-electrode body 2 is prepared that includes a negative-electrode active-material layer 22 including a powder-molded body, and a negative-electrode-side solid-electrolyte layer (NSE layer) 23 that is amorphous and formed on the negative-electrode active-material layer 22 by a vapor-phase process. The positive-electrode body 1 and the negative-electrode body 2 are bonded together by subjecting the electrode bodies 1 and 2 being arranged such that the solid-electrolyte layers 13 and 23 of the electrode bodies 1 and 2 are in contact with each other, to a heat treatment under application of a pressure to crystallize the PSE layer 13 and the NSE layer 23.