An optical measuring device includes: a screen having a reference line; a movable stage; an optical system for forming on the screen an optical image of a to-be-measured object placed on the stage; and an edge detecting sensor (112) for detecting a passage of a measurement edge of the optical image at an arbitrary position on the screen. The optical measuring device further includes: an offset value storage (143) storing a distance between the reference line and the edge detecting sensor (112) as an offset value; and a correction data calculator (144) for correcting measurement data measured with the reference line and the edge detecting sensor (112) by use of the offset value.