A workpiece mounting system mounts a sunroof member to an inner panel of a body. The workpiece mounting system is provided with a first robot, a second robot, and a control device for controlling the first and second robots. The control device performs a step of calculating as positional information the position of the sunroof member and the position of the inner panel by a CCD camera of the first robot, a step of holding and conveying the sunroof member by the first robot on the basis of the positional information and positioning the sunroof member relative to the inner panel, a step of temporarily fixing the sunroof member to the inner panel by the first robot, and a step of finally fixing the sunroof member to the inner panel by the second robot on the basis of the already calculated positional information.