A dimension measuring apparatus is configured of an imaging section that photographs a workpiece on the movable stage; a depth extending section that performs depth extension on a plurality of the workpiece images in different Z-directional positions in the movable stage, to generate a depth extended image; a master image displaying section that screen-displays as a master image the depth extended image obtained by photographing a master workpiece; a measured position information generating section that designates a position to be measured and a measuring method with respect to the master image, to generate measured position information; an edge extracting section that extracts an edge of the position to be measured from the depth extended image, obtained by photographing the workpiece, based on the measured position information; and a dimension value calculating section that obtains a dimension value of the position to be measured based on the extracted edge.