To provide an apparatus for optically and visibly demonstrating the difference of the brightness of diamond due to the superiority or inferiority of cutting.

A laser irradiation unit equipped with a laser pointer and a laser irradiation hole is provided to a main body, and a diamond cutting model piece with a predetermined thickness having the outer shape corresponding to the side surface contour of diamond is supported on a support plate. The support plate is arranged corresponding to the laser irradiation unit so as to be capable of parallelly irradiating the interior of the wall thickness of the model piece from the head table surface of the model piece. The diamond cutting model piece comprises a polygonal shape wherein a trapezoidal head and the lower part of an inverted triangle shape are integrated. At least one diamond cutting model piece is formed so that the leading end angle of the lower part of the inverted triangular shape becomes 92-97°C, and other diamond cutting model piece is formed so that the vertical angle of the leading end of the lower of the inverterd triangular shape is smaller than 92° or larger than 97°.