Disclosed is an apparatus for supporting a substrate. The substrate support unit includes a support plate having a plurality of absorption holes, in which a vacuum pressure is formed, on an upper surface thereof to absorb the substrate, and a vacuum absorption unit configured to apply the vacuum pressure to the absorption holes, and the vacuum absorption unit includes a pressure measuring member configured to measure internal pressures of the absorption holes, an intake unit configured to intake and discharge gas in the absorption holes and adjust a suction force for suctioning the gas in the absorption holes, and a controller configured to control the intake unit to adjust the suction force according to the internal pressures measured by the pressure measuring member.