PURPOSE: To provide the titled resin compsn. which produces a foamed molded article having excellent dimensional stability, surface smoothness, etc., by incorporating a specified acid amide compd. into a thermoplastic synthetic resin.

CONSTITUTION: 0.1W10wt% (based on the weight of resin) at least one aliph. acid amide compd. of formula I (wherein R1 is 10W24C aliph. hydrocarbon group; R2 is H, 1W24C aliph. hydrocarbon group, polyoxyalkylene of the formula II; R4 is 1W5C aliph. polyhydric alcohol residue; A is H, 1W24C aliph. carboxylic acid residue; n is 1W20; R3 is H, 1W7C aliph. hydrocarbon group) is incorporated into a thermoplastic synthetic resin to obtain the titled resin compsn. The compds of the formula I inhibit the escaping of a blowing agent gas from a resin foam. Examples thereof are N-stearylacetamide and N-palmitylacetamide.