A method for forming a composite material (10;50;70;80) having a corner (12;52;72;82) and a surrounding portion (14;54;74) which includes a first face portion, a second face portion, a third face portion, a first face-connecting portion, a second face-connecting portion, and a third face-connecting portion, wherein the first face-connecting portion is located along the line where the first face portion and the second face portion intersect with each other, and serves to smooth out a curve between the first face portion and the second face portion, the second face-connecting portion is located along the line where the second face portion and the third face portion intersect with each other, and serves to smooth out a curve between the second face portion and the third face portion, the third face-connecting portion is located along the line where the third face portion and the first face portion intersect with each other, and serves to smooth out a curve between the third face portion and the first face portion, the surrounding portion (14;54;74) includes the first face portion, the second face portion, and the third face portion that intersect with one another, the corner (12;52;72;82) is a trihedral angle that is located at the position where the first face portion, the second face portion, and the third face portion of the surrounding portion (14;54;74) intersect with one another, and the corner (12;52;72;82) has a smooth curved surface that is continuously connected to the first face portion, the second face portion, and the third face portion, the method comprising: a surrounding portion forming step of forming the surrounding portion (14;54;74) such that the surrounding portion (14;54;74) surrounds a through-hole existing at the position where the corner (12;52;72;82) is to be formed; a corner forming step of forming the corner (12;52;72;82) in a manner closing the through-hole; and an integrating step of integrating the surrounding portion (14;54;74) and the corner (12;52;72;82). the first face-connecting portion is located along the line where the first face portion and the second face portion intersect with each other, and serves to smooth out a curve between the first face portion and the second face portion, the second face-connecting portion is located along the line where the second face portion and the third face portion intersect with each other, and serves to smooth out a curve between the second face portion and the third face portion, the third face-connecting portion is located along the line where the third face portion and the first face portion intersect with each other, and serves to smooth out a curve between the third face portion and the first face portion, the surrounding portion (14;54;74) includes the first face portion, the second face portion, and the third face portion that intersect with one another, the corner (12;52;72;82) is a trihedral angle that is located at the position where the first face portion, the second face portion, and the third face portion of the surrounding portion (14;54;74) intersect with one another, and the corner (12;52;72;82) has a smooth curved surface that is continuously connected to the first face portion, the second face portion, and the third face portion, the method comprising: a surrounding portion forming step of forming the surrounding portion (14;54;74) such that the surrounding portion (14;54;74) surrounds a through-hole existing at the position where the corner (12;52;72;82) is to be formed; a corner forming step of forming the corner (12;52;72;82) in a manner closing the through-hole; and an integrating step of integrating the surrounding portion (14;54;74) and the corner (12;52;72;82). a surrounding portion forming step of forming the surrounding portion (14;54;74) such that the surrounding portion (14;54;74) surrounds a through-hole existing at the position where the corner (12;52;72;82) is to be formed; a corner forming step of forming the corner (12;52;72;82) in a manner closing the through-hole; and an integrating step of integrating the surrounding portion (14;54;74) and the corner (12;52;72;82).