PROBLEM TO BE SOLVED: To provide a composite segment for use in constructing a shield tunnel, which allows the emission of carbon dioxide to be reduced during manufacturing, having sufficient durability.SOLUTION: A composite segment comprises a hollow formwork 10 with an arcuate curvature formed from a plate-shaped object which contains iron, and a geopolymer composition 11 made from a silicon-containing filler and an alkali activator as raw materials. The geopolymer composition 11 is poured into the formwork 10, so that, by vapor curing or the like, the silicon contained in the geopolymer composition 11 and the iron contained in the formwork 10 make a chemical bond for fastening of the formwork 10 to the geopolymer composition 11, resulting in the formation of the composite segment.