An image processing apparatus for an endoscope, the image processing apparatus to which, any of a plurality of insertion units respectively having imaging devices with numbers of pixels different from one another being installed therein, is detachably connected and which processes an image signal captured by that imaging device and outputs the processed image signal as image data, the image processing apparatus including: an image signal processing unit that converts a pixel density of the image signal to a high density and generates a standard image signal of a predetermined amount of data.