Expanded composite polystyrene-based resin particles having a plurality of cells and cell membranes separating the plurality of cells, said cell membranes including a polystyrene-based resin forming a continuous phase and polyacrylic acid alkyl ester-based resin fine particles dispersed in said continuous phase to form a dispersed phase, and said polystyrene-based resin being complexed with said polyacrylic acid alkyl ester-based resin fine particles, wherein said dispersed phase is present in the form of a plurality of layers in a cell membrane thickness direction in a cell membrane cross-section of said expanded composite polystyrene-based resin particles.