An arylstyrene polymer comprising repeating units represented by general formula (I) [wherein R1 to R5 represent substituents containing a hydrogen atom, a halogen atom or at least one member selected from a carbon atom, an oxygen atom, a nitrogen atom, a sulfur atom, a phosphorus atom, a selenium atom, a silicon atom and a tin atom, and at least one of R1 to R5 represents an aryl group having a hydrogen atom, an aryl group having a halogen atom or an aryl group having a substituent containing at least one member selected from a carbon atom, an oxygen atom, a nitrogen atom, a sulfur atom, a phosphorus atom, a selenium atom, a silicon atom and a tin atom], said polymer having a degree of polymerization of 5 or more and a stereoregularity which is mainly a syndiotactic structure. The arylstyrene copolymer has high syndiotacticity and exhibits excellent heat resistance, chemical resistance and electrical properties. Further, the styrene copolymer has high syndiotacticity, exhibits a broad range of temperatures wherein thermoforming is feasible, and is excellent in heat resistance. Therefore, the present invention can be effectively utilized as a means for providing a heat-resistant resin, raw materials for films, etc.