To provide an end cap and a heat treatment furnace using the same capable of keeping a prescribed heat treatment atmosphere even if pressure in the heat treatment furnace is changed, and to provide the heat treatment furnace capable of performing heat treatment at a high temperature.

The end cap capable of tightly closed by a shutter member having a seal face 204, and attachable to an inlet 102 of a receiving section of the heat treatment furnace further includes a first insertion pipe 12 inserted to an inner peripheral face of the inlet 102, a groove 15 connected with the first insertion pipe around it, a first flange 20 capable of being kept into contact with the inlet 102 at a flange face 18, a second flange 24 having a flange face 25 kept into contact with the seal face 204 to be sealed, an exhaust pipe connected with a connecting section between the first flange and the second flange, and having an opening communicating with the inside of the furnace, and a seal gas introduction pipe opened into the groove and radially projecting from the connecting section.