To provide a thermal processing apparatus where a projection area perpendicular to the axis of a sealing structure and attachment structure of heat radiation heater is decreased and a chamber volume is decreased. The apparatus has a chamber for accommodating a workpiece of a thermal processing object, the chamber having a partition wall for partitioning inside from outside of the chamber, a heat radiation heater disposed penetrating the partition wall, wherein the heater has a ring seal arranged on an outer peripheral surface of the extension section, and hermetically sealing the chamber, and a heat blocking plate arranged between the heat radiation unit and the ring seal in the axial direction of the glass tube, for blocking heat radiated from the heat radiation unit to the ring seal, the heat blocking plate having an inner peripheral surface fitting along the extension section.