PURPOSE: To obtain a styrenic resin which gives a molded article excellent in gloss and impact resistance by adopting a specific production process to control the rubber content and the particle size and distribution of a rubber phase.

CONSTITUTION: A mixture contg. a styrenic monomer (e.g. styrene) and a rubber component (e.g. polybutadiene) is polymerized in a prepolymerizer 2. The resulting polymer soln. is polymerized in the first polymerizer 4 connected to the prepolymerizer 2, while a polymerizable soln. at least contg. a styrenic monomer (e. g. styrene) is polymerized in the second polymerizer 7. Polymer solns. from the first and second polymerizers 4 and 7 are combined together and polymerized in postpolymerizers 9 and 11.