The present disclosure can obtain a high-quality composite image by determining a suitable boundary when input images are sequentially stitched together to generate the composite image. An image generating apparatus 1 generates a composite image by stitching sequentially input images together. A difference value calculating section 15 calculates difference values by using the pixel values of a reference image and the pixel values of a target image that partly overlap the reference image. The difference values represent the relative relationship between the reference image and the target image. A boundary determining section 16 determines a boundary for stitching the reference image and the target image together by using the difference values calculated by the difference value calculating section 15. Then, an image compositing section 18 generates the composite image by stitching the reference image and the target image together based on the boundary determined by the boundary determining section 16.