To form a quite thick composite material having a thickness of ≥30 mm, which is two-dimensional C/C composite material obtained by using, as a reinforcing material, a carbon fiber cloth.

After subjecting the jointing surfaces of plural C/C elemental chips, which are previously carbonized or graphitized, to mechanical processing and degreasing treatment, the jointing surfaces are subjected to surface oxidation treatment by a burner. Thereafter, these C/C elemental chips are bonded with one another by using a mixture obtained by incorporating a graphite powder into a phenol resin, and the resulting material is heat cured by a hot pressing method to make an intermediate formed material. The intermediate formed material is subjected, as firing treatment, to carbonizing treatment and graphitizing treatment. Further, the resulting intermediate formed material is subjected twice, as densifying treatment, to pitch impregnation, carbonizing treatment by HIP and graphitizing treatment in this order.