A process for ion nitriding of aluminum or an aluminum alloy and an apparatus therefor, wherein aluminum or an aluminum alloy as an article to be treated is disposed on a substrate holder provided in a sealed container. A predetermined metal having an intensive affinity for oxygen is also disposed in the vicinity of the article to be treated, and a glow discharge is operated between an electrode provided in the sealed container as an anode and the substrate holder as a cathode. The electrode may be directly provided at the sealed container itself or it may be independently provided therein. According to the process and apparatus of the present invention, it is possible to form on the surface of aluminum or an aluminum alloy an aluminum nitride layer having an intensive adhesion to a substrate thereof, high hardness and excellent wear resistance.