To obtain height/the number of stages information for objects piled in multistage by a two-dimensional image acquiring means, and to take out the objects utilizing this information.

A CCD camera 20 is set above a feeding position of works 50 in multi- piled state. An image processing device 30 transmits a photographing instruction to the camera 20 to acquire the two-dimensional image of the work (top stage) 50, and the position and attitude of the work 50 and the size of the work image are found. The stage number/height is determined from the size of the work image by use of a relational table or relational expression of stage number/height preliminarily determined and stored. When the types of works are two or more, a mark M may be read to select the relational table/relational expression by preliminarily storing the relational tables/relational expressions by types. The found number of stages/height is transmitted to a robot controller 10, and a robot 40 is moved to a corrected taking- out position by use of the data to take out the work from the pile. The camera 20 may be loaded on the robot 40. This detector can also detect whether the number of stages number is a prescribed number or less or the maximum height when a plurality of piles are the subject of work.