To provide a underwater working method which enables work at a site necessary for work irrespective of a tide level for the working method applicable to work such as welding or the like below the surface of the water for a steel pipe laid under the water.

A working can 20 is suspended so as to slightly incline backward of a steel pipe 10, the working can 20 is lowered until it is partially sank in the water, and the working can is moved toward the steel pipe 10 to make a sealing section 24 abut on the surface opposed to the steel pipe 10 in the whole surface by lifting the working can with a turn-buckle 58. Water between the working can 20 and the steel pipe 10 is pumped out by a pump 29, the working can is adhered to the surface opposed to the steel pipe by water pressure, and a worker goes down a space 65 to be pumped out to carry out welding or the like of reinforcement to the steel pipe 10.