The purpose of this paper is to solve the Maintenance Cost Leveling Problem in an electric power system, which means to level annual maintenance cost for a fixed period. An ideal maintenance model is defined to solve the problem. The model is the hierarchical maintenance model with two sheaves, the equipment maintenance model and the company maintenance model. The models can explain the maintenance operations in detail and make clear the maintenance structure in the problem. The problem is divided two optimization sub-problems with a hierarchical relation by using the models. The hierarchal optimization problems can be solved approximately. This paper will show that the ideal maintenance model is effective through solving the problem. (7 pages)