1. A welding condition monitoring device for monitoring a welding state of a welding work portion by taking an image thereof by an image sensor, which device has a means for selectively emphasizing outputs of the image sensor for any of luminance areas of the image by using an output-characteristic conversion table for the image sensor, whereby outputs relating to a high luminance welding portion and outputs relating to a low luminance bead portion area emphasized respectively to increase a contrast between the currently welding portion and the already formed bead portion in the image, and outputs relating to an area between the high luminance welding portion and the low luminance bead portion area is fixed to a constant level.