1. An image segmentation method which pinpoints one of the regions from an input image belonging to the same category and identifies the one region as an image segmentation region, said method comprising: a preparation step of including, an initialization step of putting, into a non-excitation state, a cell which is an individual image segmentation unit corresponding to pixels of the input image, a taking step of pixel values of the pixels corresponding to the cell, and calculating each coupling weight between a plurality of adjacent cells, and a determination step of leader cells (self-excitable cells candidate) based on each calculation result; a self-excitable cell detection step of selecting one of the leader cells determined by the determination step to detect the one cell as a self-excitable cell; a self-excitation step of putting, into an excitation state, the self-excitable cell detected in the self-excitable cell detection step; an excitable cell detection step of detecting an excitable cell from adjacent cells based on said coupling weights between the cells in the excitation state including the leader cell and the adjacent cells; an excitation step of putting, into an excitation state, the cells detected in the excitable cell detection step; and an inhibition step of putting, into an inhibition state, the cell in the excitation state if no cell is detected in the excitable cell detection step, wherein: image segmentation of one region is completed by repeating the excitation step until no cell is detected any more in the excitable cell detection step; and the image segmentation of all the regions is completed by repeating the respective steps until no leader cell in the non-excitation state is detected any more in the self-excitable cell detection step.