A collimator 111 for an input light, a collimator 112 for an output light, a collimator 113 for a branched light, a collimator 114 for an inserted light and a wavelength selecting filter 115 are provided on a common substrate 130, and mirrors 121 to 124 for correcting an optical path or prisms XXXX to XXXX capable of producing the same advantages are provided on the optical paths between the collimators 111 to 114 and the wavelength selecting filter 115 respectively. By adjusting the mirrors or prisms, the shift of the optical axis between the collimators is corrected.