To provide one set of the optical submarine branching device to branch many desired wavelength bands.

An optical circuit unit is contained in a case 60. Optical circulators 72, 74 are mounted on one face of a base plate 62 of the case 60. A caption 76 depicts a splice part of a fiber. An optical isolator 66 and a plurality of fiber gratings 64 are mounted on the other side of the base plate 62, the fiber gratings 64 act like an optical filter that reflects a light with a prescribed wavelength and transmits the light of other wavelength bands. Captions 68, 70 indicate splice parts of the fiber. Both sides of the case 60 are covered by a transparent plastic cover to completely contain an optical circuit unit 58 in the case 60.