a point light source including a white light-emitting diode;

a collimator lens for forming a parallel beam as a result of causing light emitted from the point light source to be incident upon the collimator lens, said collimator lens being configured to direct the parallel beam at an external edge of a semiconductor wafer, an optical axis of the parallel beam being parallel to a face of the semiconductor wafer, the semiconductor wafer having a length longer than a thickness of the semiconductor wafer in a direction of the optical axis of the parallel beam;

a telecentric lens device, including two-side telecentric optics or object-side telecentric optics, for being irradiated with the light of the parallel beam that has passed the external edge of the semiconductor wafer to be measured from the collimator lens; and

an image sensor for directly receiving thereon a two-dimensional image of the external edge of the semiconductor wafer produced by the light of the parallel beam that has passed through the telecentric lens device,

wherein the light that has passed through the telecentric lens is not split before being received by the image sensor.