PURPOSE: To ensure enough calorific value by a structure wherein an array of group laminatedly arranged radiating members and semiconductor elements is energized from one end in laminated direction to the other end and adjoining radiating elements are insulated with each other while being connected to different poles.

CONSTITUTION: Holding plates 11 and 11, the radiating members 12 and PTCs (semiconductor element with positive temperature coefficient) 13 are provided at a heat source unit 7 and as well as energizing pieces 15 are provided at edges in both sides normal to the direction of draft of the holding plates 11. Furthermore, one of the adjoining radiating members 12 and 12 is rendered to be brought into contact with the upper side holding plate 11, while the other of the adjoining radiating members 12 and 12 is brought into contact with the lower side holding plate 11, resulting in making the radiating members 12 and 12 become alternately different poles to each other. In such a structure as mentioned above, when an electric current is applied between lead wires 20A and 20B, the current flows from one of the holding plate 11, the radiating member 12 and the PTC13 to the others of said plate, member and PTC, resulting in causing each of the PTC13 to generate heat in order to heat the blast flowing through air passages 22 and consequently generating hot air effectively.