Sensor(s) may be such that light-projecting component(s) and light-receiving component(s) are arranged therein. Furthermore, such sensor(s) may be provided with optical path varying means varying projected light optical path(s) and/or received light optical path(s) so as to physically vary overlapping zone(s). Such optical path varying means may carry out adjustment of optical sensitivity by increasing extent(s) of overlapping zone(s) when carrying out detection with respect to zone(s) distant from such sensor(s) and/or decreasing extent(s) of overlapping zone(s) when carrying out detection with respect to zone(s) proximate to such sensor(s).