This invention provides a side-chain-type polymer electrolyte exhibiting high ionic conductivity and a lithium secondary battery using the same. Such side-chain-type polymer electrolyte comprises a polymer structural unit represented by formula (1): wherein Rp represents an organic group obtained via polymerization of monomer compounds containing polymerizable unsaturated linkages or a polymerized organic group containing C, H, N, and O; m represents a value smaller than the polymerization degree of Rp; Y represents an organic group that binds to Rp; R1 represents a C1-10 alkylene group that allows Y to bind to Z; and Z represents a functional group having coordination ability with respect to a cation, provided that Z forms a coordination bond with a cation, wherein the polymer electrolyte has composition wherein a cation is added to a polymer having a side chain consisting of R1 and Z binding through Y to a polymer main chain consisting of Rp.