A laser welding method for a secondary battery, the method comprising: performing laser welding on a positive electrode base having a thin-film shape in which a plurality of positive electrode base tabs are formed at a side, a negative electrode base having a thin-film shape in which a plurality of negative electrode base tabs are formed at a side, and a thin-film multi-tab to be joined to each of the positive electrode base and the negative electrode base, wherein a welded portion in which the multi-tab is welded with the positive electrode base and the negative electrode base is melting-joined by using a laser such that a plurality of welding spots is formed on the welded portion , characterized in automatically determining whether the welded portion is defective while the welded portion sequentially passes through a perforated defect inspection device and a back bead inspection device , wherein the perforated defect inspection device comprises a backlight configured to irradiate the welded portion with light in a direction from a first surface toward a second surface opposite the first surface of the welded portion , image equipment arranged at an opposite side of the welded portion from the backlight to collect light transmitted through the welded portion and form a first inspection image, and a controller configured to determine whether a perforated defect of the welded portion exists by analyzing the first inspection image, and wherein the back bead inspection device comprises a front light configured to irradiate the welded portion with light in a direction from the second surface toward the first surface of the welded portion , image equipment arranged at a same side of the welded portion as the front light to collect light reflected by the welded portion and form a second inspection image, and a controller configured to determine whether a back bead defect of the welded portion exists by analyzing the second inspection image. performing laser welding on a positive electrode base having a thin-film shape in which a plurality of positive electrode base tabs are formed at a side, a negative electrode base having a thin-film shape in which a plurality of negative electrode base tabs are formed at a side, and a thin-film multi-tab to be joined to each of the positive electrode base and the negative electrode base, wherein a welded portion in which the multi-tab is welded with the positive electrode base and the negative electrode base is melting-joined by using a laser such that a plurality of welding spots is formed on the welded portion , characterized in automatically determining whether the welded portion is defective while the welded portion sequentially passes through a perforated defect inspection device and a back bead inspection device , wherein the perforated defect inspection device comprises a backlight configured to irradiate the welded portion with light in a direction from a first surface toward a second surface opposite the first surface of the welded portion , image equipment arranged at an opposite side of the welded portion from the backlight to collect light transmitted through the welded portion and form a first inspection image, and a controller configured to determine whether a perforated defect of the welded portion exists by analyzing the first inspection image, and wherein the back bead inspection device comprises a front light configured to irradiate the welded portion with light in a direction from the second surface toward the first surface of the welded portion , image equipment arranged at a same side of the welded portion as the front light to collect light reflected by the welded portion and form a second inspection image, and a controller configured to determine whether a back bead defect of the welded portion exists by analyzing the second inspection image. <EOS>