[Project] To provide a microphase-separated structure which comprises a vast and visible structure showing a structural color with the use of the phase separation due to the self-assembly of a block copolymer, enables the design of a definite structural color by a convenient method and shows temperature response.[Means for Solving Problems] A microphase-separated structure comprising a block copolymer, which contains at least a block chain A consisting of a monomer A as a repeating unit and a block chain B consisting of a monomer B as a repeating unit, and a solvent, wherein the solvent has a temperature zone 1 where the block chain A and the block chain B are soluble and a temperature zone 2 where the block chain A is insoluble but the block chain B is soluble, and a structural period thereof varies by changing temperature between the temperature zone 1 and the temperature zone 2.