A solvent for polystyrene, having an excellent dissolving ability and chemical stability with no influence on the operating environment, is disclosed. A relatively simple recycling or reutilizing process of both the polystyrene foam and the solvent is also disclosed. The solvent comprises at least one member selected from the group consisting of such a glycol ether compound as diethylene glycol dimethyl ether, diethylene glycol diethyl ether or dipropylene glycol dimethyl ether, and such a fatty acid dialkyl ester compound as dimethyl succinate, dimethyl glutarate or dimethyl adipate. These compounds have a flash point of 100.degree. C. or higher, and can be made nonflammable by addition of water.