One exemplary embodiment includes a difference image generation device including a measurement unit and a scaling unit. The measurement unit measures a variation width of pixel values of a difference image signal obtained by performing subtraction processing on first and second input image signals. The scaling unit scales each pixel value of the difference image signal based on a measurement result of the variation width so that the difference image signal can be represented in grayscale using a predetermined bit width, and outputs a difference image signal subjected to scaling.