1. An image measurement device, comprising: a measurement region detector that detects a measurement region in images having disparity; a plane region acquirer that acquires a designation of a plane region in the images which is positioned at a same plane as the measurement region in the images; a measurement coordinate converter that acquires three-dimensional coordinates of the measurement region in the images by projecting the measurement region in the images onto a plane in a three-dimensional space which is converted from the plane region in the images by using a disparity value between the images having disparity; and an information calculator that calculates a measured value of the measurement region in the images based on the coordinates.