Abstract: A single wafer heat treatment apparatus in which an object to be treated placed on a susceptor supported on a heat insulating member is heat-treated by indirectly heating the object to be treated by means of heating lamps disposed under the susceptor, characterized in that a gas entry preventive member for preventing process gas from being turned about the back surface of the susceptor is provided on a peripheral edge portion of the back surface of the susceptor. With this, process gas having entered the back surface of the susceptor is consumed by the adherence of a formed film to the surface of the gas entry preventive member.