To provide a cofferdam construction method in bridge pier steel plate winding reinforcing work by efficiently and reliably performing cofferdam work in the bridge pier steel plate winding reinforcing work executed in the underwater part.

When executing bridge pier steel plate winding reinforcing work in the underwater part, a first stage steel cylindrical frame is installed on an existing caisson by a chain block hung down from a hanging metal fitting arranged on a beam of the upper part of a bridge pier 1A. Next, a second stage steel cylindrical frame is hung down on the first stage steel cylindrical frame, a third stage steel cylindrical frame is hung down on the second stage steel cylindrical frame to be mutually connected by bolts by applying a water stop seal to the connecting part of the respective steel cylindrical frames, underwater concrete 5 is placed between a temporary wall 3 arranged outside the first stage steel cylindrical frame 2 and the first stage steel cylindrical frame 2, the part between the first stage steel cylindrical frame 2 and the existing caisson 1B is blocked up by the underwater concrete 5, and water in the steel cylindrical frame 2 is changed after solidifying the underwater concrete 5.