To enable a web to travel in a heat treating chamber steadily.

In a device which blasts hot air to a web W traveling forward of the inside of a heat treating chamber to provide the web W with a heat treating work, a support roll 70 that supports the web W from the lower surface extends in the direction of the web width. At each predetermined interval in the direction that the web travels, the front side of the support roll 70 is provided with a front side hot air nozzle 58 which is open forwardly and extends in the direction of the web width. The back side of the roll 70 in the lower part of the traveling path of the web W is provided with a back side hot air nozzle 58 which is open backward and extends in the width direction. At the front side nozzle 58, a front side guide plate 62, which guides the hot air forwardly in the horizontal direction or slightly obliquely downward and forward, is extended, and at the back side nozzle 58, a back side guide plate 64, which guides the hot air slightly obliquely downward and backward, is extended. Both the front side hot air nozzle and the back side hot air nozzle exist lower than at least the top 70a of the support roll 70.