1. A three-dimensional image measuring apparatus comprising: an XYZ shaft transfer means mounted onto a base member; a work stage mounted to the base member, for moving a measuring object to a measuring position and thereafter supporting it and having a predetermined reference surface set at a side thereof; an image obtaining means in which it is moved toward X,Y and Z shafts by the XYZ shaft transfer means, scans a grating image by the frequency of N times to a side of the measuring object supported and fixed to the work stage, obtains the changed grating image by the measuring object by N times and alternately, scans the grating image by the frequency of N times to the other side of the measuring object, obtains the changed grating image by the measuring object by N times; a light emitting means mounted to a side of the image obtaining means for generating and emitting light with a predetermined wavelength; and a control unit which, by controlling the work stage and the XYZ shaft transfer means, irradiates light generated from the light emitting means mounted to a side of the image obtaining means to the reference surface set the side of the work stage, thereafter receives the reflected light image through the image obtaining means, measures a vertical distance, thereby maintaining a focus distance between the measuring object and the image obtaining means constantly, and receives the changed grating image obtained from the image obtaining means, thereby producing the three-dimensional image.