To assemble a front panel and an aperture grill structure with high accuracy through rationalized processes.

A front panel 3 provided with a plurality of mounting pins 12 and an aperture grille structure 10 provided with a plurality of mounting spring pieces 11 corresponding to the mounting pins 12 are assembled with high accuracy. The front panel 3 and the aperture grille structure 10 are assembled together through the process of securely positioning the aperture grille structure 10 on a twist-correcting positioning jig 20 while correcting twisting components, the process of obtaining correction data by measuring the twisting components of the front panel 3 and the mounting accuracy of the mounting pins 12, the process of moving false mounting pins 27 corresponding to the mounting pins 12 on the basis of correction data to adjust and set the pins 27 relative to the aperture grille structure 10, and the process of mounting the mounting spring pieces 11 to the aperture grille structure 10 in accordance with the false mounting pins 27.