Method for displaying measurement effective area in three-dimensional visual sensor and three-dimensional visual sensor

One of stereo cameras is set such that a front view of a support surface of a workpiece is imaged, an image produced by the camera is displayed, and a range of an area where measurement processing is enabled is assigned by a rectangular frame. A manipulation assigning an upper limit and a lower limit of a height measurement range is accepted. When each assignment is fixed, zero is set as a z-coordinate to each constituent pixel of an image to which the rectangular frame is set, and a z-coordinate based on the upper limit of the height measurement range and a z-coordinate based on the lower limit are set to coordinates corresponding to the rectangular frame. Perspective transformation of three-dimensional information produced by the setting is performed from a direction of a line of sight set by a user, a produced projection image is displayed on a monitor.