Apparatus for treating substrate and method for detecting state of substrate

The inventive concept provides a substrate treating apparatus. The substrate treating apparatus includes a plurality of treating chambers performing a respective treatment on a substrate therein; a transfer chamber having a robot transferring the substrate between the plurality of treating chambers; a detection unit mounted on the robot and configured to detect a substrate state; and a controller for controlling the detection unit, wherein the detection unit comprises: an imaging member for imaging the substrate; and a driving member for moving the imaging member, and wherein the controller controls the detection unit to image and store an image of the substrate at an optimal position and determines whether an image of the substrate is a normal state based on the image obtained in the optimal position, the optimal position determined based on a process variable of the treating chamber.