A positioning apparatus includes: a calculation unit that calculates an amount of deviation between a position of a feature point of a reference workpiece and a feature point of a workpiece by comparing a relative position of an imaging unit with respect to a table when the workpiece is imaged by the imaging unit with a reference relative position, and comparing a position of a feature point of the workpiece in the image of the workpiece imaged by the imaging unit with a reference point image position; and a program changing unit that generates a correction amount such that the amount of deviation calculated by the calculation unit becomes zero, and thereby changes a program of the machine tool.