PURPOSE:To improve durability, to reduce the generation of distorsion and to improve the reliability of quality by forming a cam portion and a journal portion by solid casting using soft nitriding steel material having a specified composition, machining same and applying soft nitriding treatment to same. CONSTITUTION:A cam shaft 8 has a cam portion 9 and a journal portion 10 which are formed by solid casting. In this case, the cam portion 9 and the journal portion 10 are formed by solid casting using soft nitriding steel material set in such a manner that C: 0.1-0.6%, Cr: 0.05-2. 5%, Al : 0.2%max, V: 0.03-0.25%, Mo: 0.25% or less). Thus both a cam surface and a rotary shaft are excellent in wear-resistance, seizure-resistance and pitching resistance, and the generation of distorsion after soft nitriding treatment can be reduced so as to obtain stable quality.