To provide a solid polyelectrolyte having high lithium ion conductivity even at near room temperature and stability kept with the passage of time, and suitable for a secondary battery.

The solid polyelectrolyte contains polymerizable monomers which has functional groups having polymerizing property, and composed of solid salt composed of identical atoms having charged cation part as well as and anion part. The solid polyelectrolyte has functional groups having polymerizing property, and contains polymer obtained by independently polymerizing or co-polymerizing the polymerizable monomers composed of solid salt composed of identical atoms having charged cation part and anion part as well. The solid polyelectrolyte contains alkali metal salt.