To enable a 100% inspection and to reduce a handling time of a quality control for the joined part of a metallic thin plate, contrary to the conventional method in which the thickness and the width of samples are manually measured.

In this method, a process where a joined part 10 is irradiated by a slit-shaped laser beam La in a diagonal direction and the image of a radiated laser beam Lb are picked up, a process where the coordinates of the part of the slit-shaped laser beam Lb whose luminance is the maximum among the picked up images is detected, and a process where the quality control is executed by determining a joined quality by detecting an image characteristics having a correlation with the joined quality from the coordinates and comparing it with a reference value are included, when the quality control is executed by determining a joined quality after plural sheets of metallic thin plates 8 and 9 are laminated and located between an anvil having a pair of blades extendably held in such a manner that the upper end face is a little protruded from the upper face of a table part at the both sides of the table part and a punch oppositely located above the anvil, a punching work is executed at a part of metallic thin plates 8 and 9 by cooperation of the anvil and the punch, and the metallic thin plates 8 and 9 are joined and integrated by rolling.