PURPOSE: To assure welding strength by increasing the contact area of parts to be welded to an optical module and a module case.

CONSTITUTION: This optical module is formed by optically coupling an optical element used for optical communication, etc., via a lens 2, etc., to an optical fiber 4. The optical module has a cylindrical hollow build-up part 10 for fixing parts on the side face of the module case 1 and has a structure to weld and fixed optical parts, such as optical 4, to this cylindrical end. The contact area of the parts 5, 10 to be welded with each other is increased by increasing the thickness d of at least the contact end of this cylindrical hollow build-up part 10.