The inventive concept provides a bake unit. The bake unit comprising: a housing having an upper cover and a lower frame, the upper cover and the lower cover in combination providing a treatment space for heat treatment of a substrate; a heater provided in the treatment space for heating a substrate placed thereon; a heater cup configured to surround the heater; and a first purge gas supply unit for providing a first purge gas flow to block inflow of outer air through a gap between the lower frame and the heater cup.