A method for detecting a center of substrate, for transporting a substrate, a substrate transporting unit, and a substrate treating apparatus are provided. The substrate center detecting method includes detecting four edge positions of the substrate, judging whether a notch exists among the four edge positions or not, moving the substrate when there is a notch among the four edge positions, and calculating a center of the substrate, wherein the calculating includes re-detecting four edge positions of the substrate, calculating a first midpoint of the substrate using three edge positions out of the four edge positions of the substrate detected in the detecting, calculating a second midpoint of the substrate using three edge positions out of the four edge positions of the substrate detected in the re-detecting, and determining a real midpoint of the substrate based on moving status of the first and second midpoints of the substrate.