The invention provides a substrate
processing apparatus and a substrate
processing method, which can properly detect the edge position of a transparent substrate. The substrate
processing apparatus includes a light sensor (46) and a
control unit. The light sensor projects and receives inspection light at detection positions (P1, P2) on an advancing and retreating path of the substrate (W), and outputs a light blocking
signal when the light receiving amount of the inspection light is lower than a threshold value. When the substrate (W) is separated from the detection position (P1), the
control unit detects the position of the edge (E) of the substrate (W) on the basis of the end portion of the light blocking
signal. Furthermore, when the substrate (W) approaches the detection position (P2), the
control unit detects the position of the edge (E) of the substrate (W) on the basis of the start end of the light-blocking
signal. As a result, the position of the edge of the substrate can be detected on the basis of the signal of the portion closest to the outside of the substrate (W) among the light blocking signals output near the edge (E) of the substrate (W). Therefore, the position of the edge of the transparent substrate can be properly detected.