Provided are a high-polymer material and a method for producing a high-polymer material having high heat resistance, a high degree of isotropy in resin properties, and small variations in resin properties, because of the high degree of crystallinity, small variations in the degree of crystallinity, and the three-dimensionally isotropic crystallinity of the high-polymer material. Disclosed is a method for producing a high-polymer material by maintaining or raising the pressure during cooling, the method involving: a step of preparing a thermoplastic resin melt by heating a thermoplastic resin to a temperature higher than or equal to the melting point found from the melting peak measured by DSC; a step of applying a pressure higher than the atmospheric pressure to the thermoplastic resin melt; a step of starting cooling while subjecting said thermoplastic resin melt to pressures higher than the atmospheric pressure; and a step of releasing the pressure after cooling to a cooling end temperature that is below the upper-limit temperature of the crystallization temperature range. Also disclosed is a high-polymer material produced by the aforementioned method.