To provide an end section widening method for an existing bridge capable of expanding an end section in width for securing a right turn lane or the like, with the existing bridge kept in use.

An abutment section supporting the end section 1a of the existing bridge 1 is expanded to form an abutment expansion section 21, and an expansion lower chord 23 is suspended between the abutment expansion section 21 and the expansion base end section of the existing bridge 1. A truss expansion main truss 24 is provided between the expansion lower chord 23 and the existing bridge to connect them, then members 13 and 14 of the existing bridge becoming obstacles of traffic are removed. The work is mainly performed on the outside of the existing bridge, not on the existing bridge, and the existing bridge can be expanded in width while kept in use.