Path planning is one of important topics in robotics. When the mobile robot is building the map, it is better to use the higher resolution map in order to build a precise map. However, after the map building, if the resolution of the built map is very high, it takes much computational memory and time to perform the path planning. To realize the effective path planning, we use a multi-resolution map. The multi-resolution map can be updated by the operators suitable to a specific aim. The first aim is to represent the occupied or empty cells in the built map. The next aim is to represent the unknown areas in the built map. These are used for the path planning. The path planning is based on potential field method. The path planning uses steady-state genetic algorithm in order to set up the sub-target points. The experimental results show the effectiveness of the proposed method.