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.