PURPOSE: To carry out heat-treatment of a yarn in high response in the high- speed false-twisting work by transporting a yarn in non-contacting state close to a porous ceramic hot-plate heated with a gas burner.

CONSTITUTION: In a false-twisting heater 1, the combustible gas supplied through a line 3 is mixed with air supplied through a line 4 in a mixer 5 and the mixture is passed through a mixing gas chamber 6 and supplied to a hot plate 8 made of a porous ceramic material and acting also as a burner. A heat- insulation cover 11 having a slit 10 is attached above the hot plate 8 to form a yarn-passing path 9. The hot plate 8 is heated by the combustion of the mixed gas and the yarn Y is passed through the transfer path 9 in a state close to but separated from the hot plate 8. A gas stream is generated along the transfer path 9 by a suction mechanism placed above the transfer path. The yarn is heat-treated in high efficiency by the infrared heating with the hot plate 8 and the heat conductance through the hot exhaust layer.