Composite resin particles including: a polyethylene-based resin and a polystyrene-based resin, wherein the polyethylene-based resin and the polystyrene-based resin are included in the ranges of 50 to 20% by mass and 50 to 80% by mass respectively, with respect to the total of these resins, the polyethylene-based resin is composed of: a first polyethylene-based resin having a medium density to a high density in the range of 925 to 965 kg/m3; and a second polyethylene-based resin which is linear and which has a lower density than the first polyethylene-based resin, and the first polyethylene-based resin and the second polyethylene-based resin are included in the ranges of 90 to 30% by mass and 10 to 70% by mass respectively, with respect to the total of these resins.