An image processing device and an image processing method capable of clarifying a specific region, especially a stained region of the cell nucleus, by correcting in consideration of overlap of staining, thereby making discrimination easy, and a pathological diagnosis assistance system using the same are provided. A pathological stained image is decomposed into dye concentration images of respective dyes, dye information on the respective staining dyes are correlated, and the respective dye concentration images are corrected to emphasize a specific region.