Method of Controlling Surface Treatment System

Provided is a system controlling method that improves versatility of a surface treatment system. In the treatment system, for treating a surface of an object by a treatment machine while moving the treatment machine relative to the surface of the object by an action of a work robot, there is provided a trackless type work machine mounting the work robot on a self-propelled cart; and the work machine mounts a robot moving device for moving the work robot relative to the self-propelled cart at least in a height direction. A work area in which the object and the work machine are present is image-captured by a position determination camera. A control device recognizes relative positional relation between the object and the self-propelled cart based on image-captured data of the position determination camera and controls the self-propelled cart based on the recognized relative positional relation, whereby the work machine is moved to a designated work position near the object.