To easily bury a metallic core material into an external facing material when a composite material in which the metallic core material and the external facing material composed of a woody material are connected so that the core material is buried into the external facing material is used as a mullion 10 for a curtain wall W forming the exterior wall section of a building B.

An inside mullion member 11 placed on the indoor side of the mullion 10 is used as a composite material, and the external facing material 20 of the mullion member 11 is composed of divided sections 20a and 20a divided into two in the horizontal cross direction. Fitting recessed sections 21, into which approximately the half sections of the mullion core material 12 consisting of a hollow extrusion material made of aluminum are fitted, are formed to the opposed surfaces of each divided section 20a, both divided sections 20a and 20a are joined integrally into the fitting recessed sections 21 of each divided section 20a under the state, in which approximately the half sections of the core material 12 are fitted, and the core material 12 is buried into the external facing material 20. Recessed groove sections 23 and 24 are formed to the fitting recessed sections 21 of each divided section 20a, the recessed groove sections 23 and 24 are formed in a tapered shape that groove widths are narrowed towards the bottom side while fitting projecting strips 14 and 15 with slipping-off preventive sections 18 are formed to the exterior wall surface of the core material 12 and the fitting projecting strips 14 and 15 are fitted and fixed integrally to the recessed groove sections 23 and 24.