Copolymerized polyester resin

The present invention is a copolymerized polyester resin which contains a dicarboxylic acid component and diol components as constituting components, wherein 90 mol% or more of terephthalic acid is contained as the dicarboxylic acid component, 39 to 79 mol% of ethylene glycol, 20 to 60 mol% of neopentyl glycol and 1 to 5 mol% of diethylene glycol are contained as the diol components, the reduced viscosity of the resin is 0.50 dl/g or more, the number of contaminants each having a particle diameter of 5 [mu]m or more is 100 particles or less per 1 mm2 when a sample of the copolymerized polyester resin which has a thickness of 0.8 to 0.9 mm is produced and the sample is observed using a phase-contrast optical microscope. The copolymerized polyester resin has a higher degree of clarification than those of the conventional known copolymerized polyesters and also has excellent color hue and heat resistance.