Nucleating agent, polyolefin-based resin composition containing same, and molded article thereof

A polyolefin resin composition, comprising a nucleating agent in an amount of 0.001 to 10 parts by mass with respect to 100 parts by mass of a polyolefin resin, the nucleating agent, comprising:

• a compound represented by the following Formula (1):
• wherein in Formula (1), R1 to R4 each independently represent a hydrogen atom or a linear or branched alkyl group having 1 to 9 carbon atoms;
• R5 represents an alkanediyl group having 1 to 4 carbon atoms;
• and M represents a sodium atom,
• and a compound represented by the following Formula (1′):
• wherein in Formula (1′), R1 to R4 each independently represent a hydrogen atom or a linear or branched alkyl group having 1 to 9 carbon atoms;
• R5 represents an alkanediyl group having 1 to 4 carbon atoms;
• and M represents a hydrogen atom,
• wherein a mass ratio of phosphorus atoms and sodium atoms in the nucleating agent, P/Na, is in a range of 1.350 to 1.500.