PURPOSE: To provide the subject heater permitting the passage of a yarn and having an uniform temperature distribution by disposing a false twister and a twist-fixing radiation heater between feed rollers, the twist-fixing radiation heater having a radiating part and being equipped with a heat-shutting-out pipe, and disposing an inner air flow-producing means in the heat-shutting-out pipe.

CONSTITUTION: In a drawing and false-twisting machine in which a false twister and a heater for fixing the twisting of a yarn are disposed between a pair of feed rollers, a radiation heater 11 having a radiating part 18 is used as the heater, and a heat- shutting-out pipe 23 capable of being inserted into or withdrawn from the radiating part 18 is disposed. A means for producing an air flow in the heat-shutting-out pipe 23 is attached to the heat-shutting-out pipe 23. When a yarn Y is passed, the heat- shutting-out pipe 23 is inserted into the radiating part 18, and when the machine is continuously operated, cold air is made to flow through the pipe 23 by the inner air flow-producing means 25 to employ the pipe also as a cooling member. The heat- shutting-out pipe 23 does not hinder the space. When the heat-shutting-out pipe 23 is withdrawn from the radiating part 18 before or after the start-up of the machine, the yarn Y is uniformly heated in the radiating part 18 and the yarn is surely and easily passed.