1. An image processing apparatus, comprising: a display part that displays an image of a measuring object as an object image based on first image data, and displays a measuring portion designating image corresponding to a specific portion of the object image based on second image data; a storage part that stores a preset positional relation between the measuring portion designating image and a detecting region for detecting a predetermined characteristic portion from the object image; and a process part that manually moves the measuring portion designating image relatively to the object image, detects the characteristic portion in the object image from the detecting region having the positional relation stored in the storage part with respect to the measuring portion designating image after movement when the measuring portion designating image is moved to the specific portion of the object image, and calculates a geometrical physical quantity concerning the detected characteristic portion based on the first image data.