For use in forming a web W into a tubular shape, and heat-sealing an inner surface of outer edge of the web and an outer surface of inner edge of the web to provide a lap, a web heating device for heating the outer edge inner surface of the web with hot air before heat-sealing comprises transport means for transporting the web W along a predetermined path, a nozzle 27 having hot air outlet openings 67 directed outward as opposed to the outer edge inner surface of the web W to be transported by the transport means, and a baffle plate 32 so disposed as to be opposed to the hot air outlet openings 67 with the outer edge of the web W positioned therebetween.