Abstract: The invention relates to an installation for welding metal bands comprising two retaining members (2, 2′) for the ends of both bands, mounted respectively on a fixed frame (1) and a mobile frame (1′), means for shearing both facing parallel edges (m1, m2) on the ends of both bands (M1, M2) and electric power supply means (3) for flash butt welding of the said bands. According to the invention, the electric power supply means of both bands comprise a direct current generator (3) connected to continuous modulation means (34) of the voltage applied between the retaining members (2, 2′) in relation to the sizes of the bands (M1, M2) in transversal section and according to the nature of the metals to be welded.