The measuring unit computes at least one of an area and a perimetrical length of a polygon, based on three or more measuring points including an indeterminate point of which a position is changed by a move instruction input through an operation unit, wherein the measuring points are designated on the image by an instruction of a user input through the operation unit. The controller updates the position of the indeterminate point, when the move instruction is input through the operation unit after display the computational result, controls the measuring unit to recompute at least one of the area and the perimetrical length of the polygon based on the measuring points including the updated indeterminate point, and controls the display unit to display at least one of the recomputed area and the recomputed perimetrical length of the polygon, as recomputational result after updated the indeterminate point.