The invention provides a wavelength selective optical device in which a light emitted from an end surface of a first optical fiber that propagates optical signals with a plurality of multiplexed wavelengths is incident on a first end surface of a first graded index rod lens, then a parallel light beam emitted from a second end surface of the first graded index rod lens is incident on an optical filter arranged to face to the second end surface of the first graded index rod lens, and then a light reflected by the optical filter is incident again on the second end surface of the first graded index rod lens so as to couple to a second optical fiber arranged on a first end surface side of the first graded index rod lens, wherein a refractive index distribution constant of the first graded index rod lens is set such that a center wavelength of the light reflected by the optical filter is positioned within a desired range.