To reduce vibration during transfer and maintain the degree of freedom of a moving speed in respective zones in a furnace by a method wherein annular rails, guiding a hearth member to freely run, are arranged so as to be passed through respective heat treatment zones while a plurality of driving means, driving the hearth member into one direction, are provided individually in respective heat treatment zones.

A furnace body 1 is provided with a guide means 10, consisting of a pair of annular rails 11, continuously on an internal space 5 and an opening 2 so as to guide a plurality of hearth members 12 runably. A plurality of driving rollers 20, contacted with the inside surface of the base unit of the hearth members 12, are arranged inside of the annular rails 11. The rollers in respective zones are connected to motors, provided in respective zones, through connecting means. Accordingly, the passing speed of hearth members 12, passing through respective zones, can be set by regulating the rotating speed of the motors.