There is provided an optical fiber device including two optical fibers, rod lenses, and an optical functional element. The two rod lenses have the same refractive index distribution and the front face of each is respectively formed, at the approximate midpoint of a position where the mode field diameter of the propagating light emitted from the optical fiber and propagating through the interior of the rod lens forms a local maximum, and a position where the mode field diameter, in case the same rod lens is assumed to be extended in the axial direction, forms a local minimum subsequent to the aforementioned local maximum, in the propagation direction of the same propagating light, perpendicularly to the axis. Also, both front faces of the two rod lenses are arranged symmetrically with respect to a point where a beam waist is formed.