A surface property-improving agent for molded bodies made of polyolefin resins contains 50.0 parts to 90.0 parts by mass of a non-polar wax with a melting point of 50° C. to 100° C. and 10.0 parts to 50.0 parts by mass of a vinyl copolymer obtained by copolymerizing two types of monomers (b1) and (b2). The sum of the non-polar wax and the vinyl copolymer is 100.0 parts by mass. The monomer (b1) is styrene and/or acrylonitrile. The vinyl copolymer contains 0.1 parts to 49.9 parts by mass of the monomer (b1) and 0.1 parts to 9.9 parts by mass of the monomer (b2) wherein the sum of the monomer (b1) and the monomer (b2) is 10.0 parts to 50.0 parts by mass. To 100.0 parts by mass of a polyolefin resin, 0.5 parts to 10.0 parts by mass of the agent is added. The monomer (b2) is a methacryloxypropyl polyorganosiloxane.