A coaxial nozzle to blow an inert gas on a part to be welded is provided, and at least one discharging nozzle to blow a compressed shielding gas around the part to be welded so as to cover the inert gas is provided at the outer side of the coaxial nozzle. Then, a laser oscillator to oscillate a laser is provided, and a condenser to converge the laser, and thus, melt the part to be welded through the irradiation of the converged laser is built in. Moreover, an evacuating nozzle to evacuate gases around the melting parts is provided.