In a wavelength selective optical device, a lens for transmitting multiplexed optical signals having a plurality of wavelengths is provided to face an end of a first optical fiber such that light output from the end of the first optical fiber is converted into parallel light, and an optical filter is provided at a location to which the parallel light output from the lens is input. A second optical fiber is provided at a location in which the light reflected from the optical filter is input to the lens again to be focused by the lens. The lens is configured by bonding the ends of two gradient index rod lenses having different refractive index distribution constants and the substantially same outer diameter to each other to align their optical axes to each other.