The welding operation monitoring system includes an image capturing device that is disposed on a side opposite to a side to which the plasma flow is supplied out of a pipe inside and a pipe outside of the strip-shaped steel sheet formed in a tubular shape, and is configured to capture a color image including a plasma flow over the V-shaped region; and a welding operation monitoring device that is configured to generate a specific color component image obtained by extracting a specific color component from the color image, and specifies a V-shaped display region, which is a region corresponding to the V-shaped region within the color image, on the basis of the V-shaped region shown in the specific color component image, thereby analyzing a state of the welding operation.