To provide a self travelling washing robot device, which runs on a transparent external wall surface of a multistory building smoothly in the transverse direction.

A self-travelling type transversely traveling robot 3 for washing the external wall surface 1 of a building is fitted on and supported by transversely stretching groove-shaped guide rails 2 furnished at two stages up and down on the external wall surface 1, and a pin rack 4 is fixed to the inner surface of each guide rail 2 as stretching parallel with the rail 2, and independently driven sprockets 5 up and down are furnished on this robot 3. The sprockets 5 are engaged to the upper and lower pin racks 4, and the number of revolutions per min. of the upper and lower sprockets 5 is adjusted to the number of pins of the upper and lower pin racks 4 so that the robot 3 does not incline aside.