1. A size measurement device for measuring a size of an object from a captured image of the object, the device comprising: an imaging unit that captures an image of an object; a display unit that displays image data captured by the imaging unit; an input unit for inputting instructions of a user; a region setting unit that, when positions are designated with the input unit in the image data displayed on the display unit, sets surrounding regions including therein respective designated positions; and a feature point determination unit that determines, in the surrounding regions set by the region setting unit, feature points providing coordinates of the object to be measured.