In recent years, in order to achieve carbon neutrality, there has been a demand for improvements in durability that contribute to the miniaturization of gear parts for large construction machinery. Since wear and seizure occur on gear tooth surfaces due to the increase in contact surface pressure and the decrease in lubricant volume that accompany miniaturization, the application of functional surface treatments such as solid lubricant films that improve wear and seizure resistance is being considered. On the other hand, since lubricant is used on gear tooth surfaces, it is necessary to clarify the friction and wear characteristics of various surface-treated steels under oil lubrication. In this study, we are evaluating the tribofilm formation process and the friction and wear characteristics of the tribofilm on the surface of steel with functional surface treatment.