The invention provides a duct mounting structure in skylight device, which can increase the rigidity of the tail of the sunshade plate rail projecting towards the back of vehicle and the rigidity of duct of cable. The said skylight device (1) comprises: cable (C1,C2) for switching the roof plate (4) through pushing and pulling; guide raill (5,5) for guiding the switch of the roof plate (4); and sunshade plate rail (20,20) for guiding the switch of the sunshade plate, wherein the duct (P1~P4) provided with optical cable (G1,G2) is set along the back of the sunshade plate rail (20) projecting towards the back of vehicle and the duct (P1~P4) is fixed back the sunshade plate rail (20).