A three-dimensional image measuring device which comprises a light source; a plane image forming unit for forming a plane image in a space in its depth direction on the basis of light emitted from the light source; a scanning unit for moving and scanning the plane image formed by the plane image forming unit in its depth direction; an object to be measured disposed in the space where the plane image is formed; a light receiving unit for measuring the strength of light scattered on a surface of the object as the plane image is moved and scanned and; a distance measuring unit for measuring the distance to the object on the basis of the output of the light receiving unit, whereby a three-dimensional image with least reduced invisible area is easily and accurately measured in a short time without using the principle of triangulation.