Abstract: In a traveling inspection robot system, two carriages are each provided with one pair of guide rollers for guiding the travel in the vertical direction and two pairs of side rollers for guiding the travel in the horizontal direction. The two pairs of side rollers are arranged such that one pair locates on each of the front and rear sides of the pair of guide rollers as viewed in the direction of advance. The two carriages are interconnected by a coupling plate through parallel steering shafts, and a sprocket and a motor for driving the sprocket are provided as travel driving device on one carriage for giving a traction force to a transversely central portion of the upper inner surface of the monorail. An antenna and a current collector are provided on the other carriage. A control circuit unit and a span and tilt mechanism are attached to the coupling plate with a sensor unit mounted to the span and tilt mechanism.