An apparatus for treating a substrate includes a process chamber having a process space therein, a support unit that supports the substrate in the process space, a heating member that heats the substrate supported on the support unit, and an exhaust unit that evacuates the process space. The exhaust unit includes an exhaust duct and a heat retention unit having a retention space that retains heat released from the process space. The retention space surrounds an adjacent area located adjacent to the process chamber in the exhaust duct.