A height-measuring device (100) in which the focal position of an image-forming optical system (20) is moved in relative fashion in the direction of an optical axis with respect to an object (10) to be measured; scanning is performed; images of the object (10) to be measured, which are formed by the image-forming optical system (20), are obtained in order; and the focal position for individual pixels of the images is found, thereby yielding a relative height value of the object to be measured (10) at positions corresponding to the pixels; wherein a second function (g) is defined on the basis of a first function (f) fitted to a numerical value sequence comprising a coordinate value on the optical axis and a light intensity value for the pixels of a plurality of the images obtained by the scanning, or the coordinate value and a numerical value obtained by processing the light intensity value; and positions on the optical axis at which a correlation value between the numerical value sequence and the second function (g) becomes a maximum value or a minimum value serve as the relative height values of the object to be measured at the positions corresponding to the pixels.