Abstract: An apparatus used for an epitaxial vapor growing arrangement and for detecting whether a wafer is properly seated within a susceptor contained therein. The apparatus includes a semiconductor laser element that generates a laser beam which irradiates the wafer's surface. The apparatus, further, includes a combination of a stop mechanism, a condenser lens and a photo diode, which detects the laser beam reflected from the wafer surface and an operation circuit, which determines the wafer's posture on the susceptor. During operation, the reflected laser beam focuses on a receiving surface of the photo diode through the condenser lens. The operation circuit then compares the output signal from the photo diode with a preset reference value for discriminating the slope of the wafer.