To provide an endless belt of a thin film whose thickness is 50 μm or smaller produced with laser beam welding.

The thin film welding equipment is provided with thin film clamping devices (5+8+7; 5+8+27+28+29) furnished with thin film holding members (5+8), having a backup plate 5 and a laser beam transmitting plate 8 which holds both side faces of the lapped part or the butted part of two thin films S whose thickness is 50 μm or smaller, and pressure welding equipment (7; 27+28+29) which pressure-welds the backup plate 5 and the laser beam transmitting plate 8, and further provided with a laser beam irradiating devices (17+21+23) having an optical system with which devices a line to be welded which is the pat to be welded of the lapped part of the two thin films S or the butted part is irradiated with the laser beam, and with which devices the part irradiated with the laser beam is welded.