YARN HEATER AND YARN PROCESSOR

Power consumption is reduced. In a first heater 13, two yarn running grooves 56a and 56b are formed to extend in an extending direction and to be aligned in the base longitudinal direction. The first heater 13 further includes a heating unit 50 which extends along the extending direction and is configured to heat yarns Ya and Yb running in the yarn running grooves 56a and 56b and a heat insulator 70 which extends in the extending direction and is provided to be opposite to the yarn running grooves 56a and 56b over open ends of the yarn running grooves 56a and 56b in an up-down direction. In the heat insulator 70, a yarn guide passage 74 is formed to allow the yarns Ya and Yb to pass through, in order to insert the yarns Ya and Yb into the respective yarn running grooves 56a and 56b. The yarn guide passage 74 is shared between the yarn running grooves 56a and 56b. The yarn guide passage 74 has a narrow portion 74a having a width W1 that is narrower than the sum of the widths (W3a+W3b) of the two yarn running grooves 56a and 56b.