A polyolefin-based resin pre-expanded particle includes a polyolefin-based resin; an organic phosphorus-containing compound being nitrogen-free; and a hindered amine having an OR group substituted directly on an N-atom where R is a saturated or unsaturated hydrocarbyl group, wherein the organic phosphorus-containing compound is at least one selected from the group consisting of alkyl phosphonic acid, an ester of the alkyl phosphonic acid, aryl phosphonic acid, an ester of the aryl phosphonic acid, a cyclic phosphonate, and a cyclic bisphosphonate, the polyolefin-based resin pre-expanded particle comprises from 1.0% by weight to 10% by weight of the organic phosphorus-containing compound and from 0.1% by weight to 5.0% by weight of the hindered amine, and the weight ratio of the organic phosphorus-containing compound to the hindered amine is from 1.0 to 20.