A wear amount measuring device includes an image display unit, an image processing unit, and a wear amount computing unit. The image display unit displays a real object image based on real object image data containing a wear amount measurement target and a reference part, and displays a plan image based on design plan data containing the wear amount measurement target and the reference part. The image processing unit executes an image processing of overlapping the real object image and the plan image at an equal scale on a corresponding positional relation when the reference parts are matched. The wear amount computing unit computes a wear amount based on a magnitude of an interval between a measurement contour line drawn along a contour of the wear amount measurement target in the real object image and a plan contour line in the plan image.