A method of manufacturing a biaxially stretched film according by: (I) preheating a thermoplastic resin film to a temperature in a rubbery plateau region in a storage elastic modulus curve; (II) biaxially stretching the thermoplastic resin film under a condition that a stretching speed is 500%/min or higher while heating the thermoplastic resin film to the temperature in the rubbery plateau region; (III) cooling the thermoplastic resin film after the biaxially stretching (II) to a temperature in a glass-to-rubber transition region or a glass region in the storage elastic modulus curve; and (IV) relaxing the thermoplastic resin film after the cooling (III) at a temperature in the glass-to-rubber transition region.