We'll present how deep learning is applied in a manufacturer's production line. Fujikura and OPTOENERGY are introducing a visual inspection system incorporating deep learning in the production process of semiconductor lasers. The same inspection accuracy as skilled workers was achieved by optimizing the image size and the hyper parameters of a CNN model. The optimized image size is less than one quarter of the image size required for the visual inspection by skilled workers, which leads to large cost reduction of the production line. It was also confirmed that the highlighted region in the heatmaps of NG images didn't meet the criteria of the visual inspection. The visual inspection incorporating deep learning is being applied to other products such as optical fibers and electrical cables.