To enable the blow molding of a chair capable of holding the surface temp. of its seat part to temp. appropriate for a user without being affected by atmospheric temp. by the heating element integrally incorporated in the seat part at the part near to the surface plate thereof.

The seat part 10 of a chair is a blow molded product composed of a single parison and a heating element 11 is integrally incorporated in the parison at a time of blow molding so as to be positioned near by the surface plate part 10a of the seat part 10. The seat part 10 of the chair is pref. composed of a hollow member 12 having an almost rectangular cross section and a plurality of ribs 13 are formed to the rear plate part 10b of the hollow member 12 so as to be turned inward and the heating element 11 being flat as a whole is brought in contact with the ribs 13 and the inner surface of the upper resin plate part of the seat 10 under pressure to be integrally incorporated in the hollow member 12.