The friction drag decreases and the friction resistance decrease ship that improves fuel cost is offered.Duct 3 is divided into two or more independent chambers 5, with partition 4 according to the longitudinal direction; piping 6 is introduced in each chamber 5 and penetrates through partition 4 to supply air to each chamber 5. Air is supplied by assistance compressor 7 through piping 6. Opening 8 is formed in the lateral aspect of each chamber 5, and microbubble generator 10 is installed in this opening 8.