A substrate treatment apparatus includes a transport part to transport a transparent rectangular substrate, a substrate support part to support the substrate, light generators to irradiate two different lights onto the moving substrate, and sense the irradiated lights, and a controller to determine a posture of the substrate with reference to the sensed lights and control the transport part such that the substrate is seated on the substrate support part in a default posture that is preset. The controller determines the posture of the transparent rectangular substrate with respect to the default posture using a time difference between a time point at which a first light of the two different lights is not transmitted through an edge of the transparent rectangular substrate and a time point at which a second light of the two different lights is not transmitted through the edge of the transparent rectangular substrate.