To provide a thin electrolyte plate with small ionic conduction resistance, and having a glass electrolyte membrane hardly damaged in a production process.

An interposing body 11 is constituted by fitting a supporting body 11a made of porous carbon having a catalyst layer 13 to a supporting body holder 11b made of dense carbon, and a interposing body 12 is constituted by fitting a supporting body 12a made of porous carbon having a catalyst layer 14 to a supporting holder 12b of dense carbon. Glass electrolyte sol is applied to a surface where the catalyst layer 14 of the interposing body 12 is made to form a glass electrolyte membrane 15. The interposing body 11 and the interposing body 12 are joined, and a plate electrolyte body 10 is formed by interposing the glass electrolyte membrane 15 through the catalyst layers 13 and 14.