Disclosed is a polyester resin composition improved in crystallization rate. The polyester resin composition comprises (a) a polyester resin and (b) a metal salt of a sulfonamide compound having a structure represented by the general formula (1): (1) wherein R and R' independently represent a hydrogen atom, a halogen atom, an alkali metal atom, an amino group, an alkyl group having 1 to 10 carbon atoms which may be branched or may have a substituent, an alkoxy group having 1 to 10 carbon atoms which may be branched or may have a substituent, or a cyclic group having 3 to 30 carbon atoms which may have a substituent, provided that R and R' may together form a cyclic group; and n represents an integer of 1 or 2.