To provide an optical passive device which is suppressed in the amount of light reflection and is easily assembled as an optical passive device equipped with an optical basic element and a collimation lens which interfaces between optical fibers at its input and output, respectively.

A lens for input and a lens 9 for output are cylindrical refractive index distribution self-focusing rod lenses which have an oblique worked surface on one end surface and a spherical worked surface on the other end surface. The end surfaces of first and second optical fibers 1 and 4 have an obliquely sheared section. A cylindrical holding member 8 to hold the optical fibers 1 and 4 is provided at the end of the fibers. The oblique worked surface of the lens 9 is brought into contact with the obliquely sheared section of the fibers 1 and 4, and those outer peripheries are fixed by a ceramic precision sleeve 10.