PURPOSE: To quicken curing and to simplify operation by arranging a cylindrical lamp of a traveling path of optical fiber, a conduit-like lamp around the cylindrical lamp, an elliptical converging mirror at the conduit-like lamp around the lamp, etc., and making the converging mirror into an elliptic cylindrical surface.

CONSTITUTION: A casing 10 for a lamp chamber, a cylindrical mercury lamp 11, a casing 20 for a work chamber, a translucent pipe 40, a converging mirror unit 50, etc., are arranged to form a device for curing a coating agent. Then, an elliptical converging mirror 31 at the lamp side is processed to constitute part of a first elliptical cylindrical surface 31A having an axial line of the lamp 11 as a first focus and a traveling path of an optical fiber F as a second focus. An elliptical converging mirror 51 at the work side is processed to constitute a second elliptical cylindrical surface 51A having the axial line of the lamp 11 as a first focus and the traveling path of the fiber F as a second focus. Then, the minor axis of the ellipse of the first cylindrical surface 31A is made larger than that of the second cylindrical surface. The optical fiber is irradiated with reflecting light advancing from the converging mirror 31 toward the optical fiber F to cure a coating agent applied to the optical fibers.