This paper discusses a general and efficient method for solving the motion planning problem defined as checking the existence of a collision-free path among known stationary obstacles, and also presents its application to a plant CAD system. The basic approach taken in this method is to restrict the free space referred to in path searching and to avoid executing unnecessary collision detections. The configuration space is equally quantized into cells by placing a regular grid, and two new search strategies which enumerate restricted cells are introduced for realizing this method. One is a local strategy which enumerates free space cells only along the boundary of the free space in the configuration space. Another is a global strategy which finds the outer boundary of the free space. This method has been actually implemented and has been applied to an example in a nuclear power plant.