An image processing apparatus includes a partial image memory unit for reading partial image data from an image pickup device and sequentially storing the partial image data. The image processing apparatus also includes an image composition unit for generating the composite image data by synthesizing the partial image data obtained from the partial image memory unit. Only when a composition incomplete signal does not exists the partial image memory unit stores the partial image data and generates a storage completion signal upon completing the storage of the partial image data. The image composition unit generates the composition incomplete signal when the composite image data is being generated, on the condition that the storage completion signal is present. The image composition unit reads at least one of the partial image data from the partial image memory unit and starts the generation of the composite image data using the partial image data when the composite image data is not being generated.