PURPOSE: To improve the heat-insulating property, enhance the heat-collecting efficiency, facilitate the positioning and improve the working property by a method wherein a heat collector is fitted to and supported by an eaves-portion transverse bar, middle-portion transverse bars and heat-insulated connecting members for a metallic roof member.

CONSTITUTION: A heat collector A is formed by inserting heat collectors 2 at regular intervals in the longitudinal direction of metallic heat-collecting plates 1, and is supported by right and left connecting members c, an eaves-portion transverse bar 24 and middle-portion trnasverse bars 38. At the supporting portions, a heat-insulating member is interposed for avoiding the contact between metallic component parts. The front end on the side of the eaves-portion of the heat collector A is automatically positioned by a notch 20 of a water injection cover 23. Accordingly, the heat insulating property and the heat collecting efficiency ar improved, the labor required for fitting is reduced and the system is made econimical.