A crystal nucleating agent for polyolefin resins includes at least a raw material crystal nucleating agent (a) as a component (A), where the component (A) may be a diacetal compound. The crystal nucleating agent may have an angle of repose of 48° or smaller, and a 1-mm-thick polyolefin resin molded article produced using the crystal nucleating agent may have a haze value of 12 (percent) or smaller as determined by a method in conformity with JIS K7136 (2000). The crystal nucleating agent may be a blend including a sulfuric acid ester salt and/or a sulfonic acid salt as a component (E) and a higher fatty acid as a component (F). The blend may be obtained by preparing a mixture of the component (A) swelled with an organic solvent, the component (E) dissolved in the organic solvent, and the component (F) and removing the organic solvent from the mixture.