In a laser module, a laser beam which is emitted from a laser element is focused by a condensing optical system and caused to enter an incidence end of an optical fiber. A laser device is provided with a plurality of these laser modules. Emission end portions of the optical fibers are bundled to form a laser emission portion. A thickness of cladding h of each optical fiber is set to a value calculated in accordance with the following equation:.times..times..ltoreq..times..times..times..times..tim- es..times..times..times..times..times..times..times..times..times..times..- times..times..times..times./ ##EQU00001## As a result, it is possible to emit a laser-beam with a high intensity that is required for functionality as a laser light source, for the purpose of raising resolution of an exposure apparatus.