To provide a straight-chain polypropylene-based resin composition excellent in surface appearance, injection foam moldability, and impact strength, allowing significant weight reduction, and also excellent in recyclability and environmental compatibility, and an injection foam molded article.

The straight-chain polypropylene-based resin composition contains a polypropylene-based resin (A) comprising a straight-chain propylene-ethylene block copolymer (A-1) having properties (i) to (vi) and a propylene-based polymer (A-2), an elastomer (component B), and a foaming agent (component C). Property (i): A MFR (melt flow rate) of a straight-chain propylene polymer moiety is 150 g/10 min or more. Property (ii): A ratio of a straight-chain random copolymer moiety to the component (A-1) is 2-50 wt.%. Property (iii): Intrinsic viscosity [η] of the straight-chain random copolymer moiety is 5.3-10.0 dL/g. Property (iv): The MFR is more than 100 g/10 min. Property (v): A die swell ratio is 1.2-2.5. Property (vi): Strain-hardening properties are shown at an elongational viscosity measurement at 180°C.

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