To provide a device of monitoring narrow gap welding which can clearly image and monitor a welding state in narrow gap welding.

A device of monitoring narrow gap welding inserts a welding torch 20 and a wire feeder 30 in a narrow gap 101, and generates an arc between a base material 100 and an electrode member to weld the narrow gap 101, and includes a welding arc monitoring camera 60 which shoots a welding part where the arc is generated. The welding arc monitoring camera 60 includes a lens member 61 which is arranged so as to image a welding part 102 from above the narrow gap on an opposite side to the welding torch with respect to the wire feeder 30. The lens member 61 includes a lens surface 62 which is larger than a width dimension of an insertion part 32 of the wire feeder 30, and is arranged in a periphery of the wire feeder 30 so as to secure an optical path of an arc light between the lens surface 62 and the welding part.