A sheet-laminated lithium ion secondary battery comprising: a membrane electrode assembly which comprises a cathode sheet comprising a cathode current collector having formed thereon a cathode active material layer, and an anode sheet comprising an anode current collector having formed thereon an anode active material layer, the cathode sheet and the anode sheet being laminated through a separator; and a sheet outer casing having accommodated therein the membrane electrode assembly, wherein, in the membrane electrode assembly, a sheet thermoplastic resin layer is inserted as at least one of an interlayer between the cathode sheet and the separator, and an interlayer between the anode sheet and the separator.