PURPOSE: To provide the horizontally moving device of an outer wall work machine, which can execute exactly a horizontal movement to a target position of the outer wall surface.

CONSTITUTION: The outer wall work machine is constituted of a supporting frame 11. and a horizontally moving body 12, so that the horizontally moving body 12 can be moved horizontally by suspending both side parts thereof from the supporting frame 11 by a suspending link 22, and on the side part, etc., of the supporting frame 11, a ball screw 26 for executing a reciprocating motion in the vertical direction and a nut 27 are provided, so that this reciprocating motion in the vertical direction is transferred to the horizontally moving body 12 through a direction converting link 30 and it moves horizontally, and the device becomes compact by making width of a driving mechanism small. Accordingly, when this horizontally moving device 10 is applied to an automatic window wiping unit, a brush and a squeegee are moved horizontally and exactly to a prescribed position of a windowpane and unwiped portions can be decreased remarkably.