To provide dew condensation preventing frame construction of a daylighting for preventing the occurrence of dew condensation caused by difference between indoor and outdoor temperature.

Rising wall surfaces 12 and 21 of both inside and outside frames are opposed to each other at an interval without bringing the rectangular outside frame 1 into contact with the inside frame 2, a space section 5a between the upper ends of the rising wall surfaces 12 and 21 and a space section 5b between the lower ends of them are formed to inject foamable polyurethane having adhesive efficiency between the spaces 5a and 5b to make it foam, and thermalinsulating materials 4a and 4b connecting the inside and outside frames 1 and 2 to integrate them into a unit are formed without using any screw. A space section surrounded by both up and down thermal insulating materials 4a and 4b and opposed surfaces of the rising wall surfaces 12 and 21 is formed into a hollow air room 6 enclosing air therein to cut off heat conduction between both inside and outside frames 1 and 2 together with the thermal insulating materials 4a and 4b, and the occurrence of dew condensation can be prevented.