The present invention relates to an apparatus for heat-treating a substrate, and more particularly to an apparatus for substrate treatment to perform a heat treatment of a substrate for a flat panel display panel.An apparatus for substrate treatment according to an embodiment of the present invention comprises a processing chamber having a substrate treatment space; a heating housing having a heating lamp that emits radiant energy and a reflecting block that reflects radiant energy emitted from the heating lamp; and a window that maintains a sealing between the processing chamber and the heating housing and transmits the radiant energy to a substrate.