A rehabilitating pipe having a flange at one end thereof is laid inside a first existing pipe so that the flange contacts an inner circumferential surface portion of a second existing pipe surrounding a portion where the first and second existing pipes intersect. A flange part of a flanged tubular member is adhesively fixed to the inner circumferential surface of the second existing pipe so that the flange part covers the flange of the rehabilitating pipe and the inner circumferential surface portion of the second existing pipe. A tubular part of the flanged tubular member is adhered to the rehabilitating pipe to thereby seal a gap between an inner circumference of the first existing pipe and an outer circumference of the rehabilitating pipe.