Patent ID: 7747147

Claim:
A heating unit comprising: a heating element structure having a heating element, a first diathermanous tube incorporating said heating element structure, a second diathermanous tube which is penetrated by said first diathermanous tube to project the both sides of said first diathermanous tube from the both ends of said second diathermanous tube, and which is disposed so as to have a predetermined clearance from the outer circumferential face of said first diathermanous tube, and fixing means which provide the clearance between said first diathermanous tube and said second diathermanous tube, and are attached to the both end portions of said second diathermanous tube so as to prevent to move in an axial direction of said second diathermanous tube, wherein said heating element structure comprises said heating element, lead wires extended from both ends of said first diathermanous tube, and heating element holding means for connecting said heating element to said lead wires, an inert gas is sealed inside said first diathermanous tube which is sealed by sealed portions at both ends of said first diathermanous tube, portions of said lead wires are embedded in the sealed portions of said first diathermanous tube, and said fixing means is disposed at an area between a heating element side end of said sealed portion and a heating element side end of said heating element holding means in the axis direction of said first diathermanous tube.