[Problem] To reduce the length of time required to determine the position of a workpiece.
[Means to Solve Problem] The present invention includes: an imager 30; a driver 80 that causes the imager 30 to move in a relative manner, with respect to a workpiece W having a planar face Wa, in a planar direction parallel to the planar face Wa; a controller 41 that controls the driver 80 so that the imager 30 moves along a prescribed trajectory T that passes through a plurality of locations in a boundary portion Wb in the planar face Wa in a plan view; a memory storage 42 that stores image information captured by the imager 30 while the imager 30 moves along the prescribed trajectory T, and coordinate information of the imager 30 at a time of capturing each image information; a position determiner 43 that determines the position of the workpiece W in the planar direction corresponding to the boundary portion Wb, on the basis of the image information and the coordinate information stored in the memory storage 42; and an offset determiner 44 that determines an offset of the workpiece W from a reference position S, on the basis of a determination result from the position determiner 43.