To provide heat treatment in which a furnace chamber can be exhausted uniformly while preventing temperature distribution from being shifted.

A plurality of exhaust pipes 5 (5a, 5b, 5c) are inserted into a furnace chamber 3 while differentiating the insertion depth at least partially. Length of the exhaust pipe is differentiated depending on the insertion depth into the furnace chamber. The plurality of exhaust pipes are arranged, at least partially, in another exhaust pipe through a specified gap.