Abstract: Device for the semiautomatic or fully automatic electric longitudinal-seam mash resistance welding of can bodies from overlapping, cut-to-size sheet-metal blanks rolled into sidewalls (20), with a guide arranged in front of the welding site for determining the lap width of the sidewall edges (21, 22) including resilient guide elements (32-34), whereby the sidewall edges (21, 22), when traveling toward the welding site, can be pressed against the bases (29, 30) of the groove of a Z-rail (13), and with a calibrating rim (40) arranged in the zone of the welding site, with such a construction of the guide means that the lap width of the sidewall edges (21, 22) at the welding site is at most six times the thickness of the can wall, and with wire electrodes (11) that can be pulled off a reel and are guided over electrode rollers (7, 9), these electrodes being fashioned as flat-wire electrodes (11) having a width exceeding the lap width of the sidewall edges (21, 22) at the welding site.