Upon reception of a work sensing command from a robot controller, an image processing unit obtains a two-dimensional image of thee whole work pallet including a work, with a CCD camera (a first sensor means). A line of sight is calculated based on the work position on the sensed two-dimensional image. The robot controller determines the destination of movement of the robot such that a crossing line LC of slit beams LB1, LB2 of a laser sensor (a second sensor means) can agree with the calculated line of eight. The image processing unit operates the laser sensor so as to surely irradiate the laser slit beams LB1, LB2 to the target work, permitting the laser sensor to sense the three-dimensional positional and orientation of the target work.