To provide a cofferdam construction method which enables a large working space with no timbering to be easily secured on the inside of a cofferdam structure, and which enables construction to be inexpensively performed in a short period of time.

The cofferdam structure 10 comprises: a cut-off wall 12 which forms the working space around a bridge pier 52; and a reinforcing truss section 11 which is provided in a part of the outer peripheral surface of the cut-off wall 12 so as to reinforce the cit-off wall 12. The reinforcing truss section 11 is a reinforcing section with a structure in which steel materials etc. are combined together in a so-called truss shape. The cofferdam structure 10 has a constitution in which a series of annular rings is formed of an outer edge of the reinforcing truss section 11 and a portion, having no reinforcing truss section 11, of the outer peripheral surface of the cut-off wall 12. The cofferdam structure 10 is split into a plurality temporary rings, and constituted by connecting the stacked temporary rings together via a connecting portion 13.