To provide a polymer solid electrolyte for a secondary battery high in a cation transport number and conductivity.

This polymer solid electrolyte containing a polymer of a carbonate group-containing (meth)acrylic acid ester monomer represented by formula (1), and having a molecular weight not smaller than 300, and an electrolyte salt is formed. In formula (1), R1 is a hydrogen atom or a methyl group; R2 is a 1-6C alkylene group; and R3 is a phenyl group, a benzyl group, a 1-6C alkyl group, or a 1-6C alkoxyalkyl group.