To provide a duct device of a tanker which reduces effort required for maintenance, suppresses the maintenance cost, and has high traffic property and safety.

In the duct device 50 of the tanker, a duct 51 having a cross sectional area of a predetermined magnitude is disposed from a predetermined position on the stern side to the predetermined position on the bow side of a plurality of cargo tanks 20 under an upper deck 9 of the tanker 1. At least a plurality of cargo work pipes 25 and a traffic device (lifeline) 31 are disposed inside the duct 51. The steel duct 51 is disposed on the center line of the tanker 1.