PURPOSE: To promote fuel atomization in order to enable to strength of a PTC element to be sufficiently sustained, by forming the bore of a mixture stream passage hole in a tapered shape decreasing the diameter of the hole from the upstream side to the downstream side, and by forming the peripheral edge section of the lower surface opening of the hole in an acuate edge shape.

CONSTITUTION: An insulator 3 holds a disc-like PTC element 5 so that the latter partitions a mixdture passage 10 directly below a throttle valve 4. A PTC element 5 made of ceramics, generates heat when it is energized so that it is maintained at a temperature around a Curie point. A plurality of mixture stream passage holes 5a are formed in the PTC element in such a tapered shape that the diameter thereof are decreased toward the downstream side. Thus, the atomization of fuel is promoted and the strength of the PTC element is sufficiently sustained.