To efficiently prevent the freezing of an engine carburetor and heating of intake air.

A heat insulator 3 with insulating property is installed between a carburetor 1 and an intake pipe 21 on the downstream side of the carburetor 1, an annular PTC element 30 is set on the intake pipe side of the heat insulator 3 apart from the heat conductive carburetor 1 and intake pipe 21, a cylindrical heat radiation plate 31 is closely fitted to the annular PTC element 30, its cylindrical part 33 is inserted into the intake pipe 21, and a disk-shaped PTC element 42 closely fitted to the housing 2 is set on the carburetor side of the heat insulator 3. Also the positive wirings of both PTC elements 30 and 42 are molded to the inside of the heat insulator 3. In addition, the annular PTC element 30 performs the heating of intake air by the close-fitted cylindrical heat radiation plate 31, and the disk-shaped-shaped PTC element 42 heats only the carburetor 1 so as to prevent freezing. Though the negative wirings of both PTC elements 30 and 42 are installed on the outside, it does not cause any trouble due to contact, i.e., it is reliable because it is at the same potential as the carburetor 1 and intake pipe 21.