A profile measuring instrument for measuring a profile of a workpiece by rotating the workpiece, the profile measuring instrument comprising: a probe that measures the workpiece; a movement mechanism that holds and moves the probe; a rotary table to which the workpiece is fixed and which rotates the workpiece relative to the probe; a counter unit that measures a displacement of the movement mechanism; a reference gauge measuring part that measures a diameter or radius of a reference gauge based on the displacement measured by the counter unit along an axial direction in a reference gauge coordinate system set for the reference gauge while the reference gauge is fixed to the rotary table, the reference gauge having a columnar shape or cylindrical shape and having a known diameter or radius; a correction function generating part that generates a correction function based on a difference between the diameter or radius measured by the reference gauge measuring part and the known diameter or radius, when the diameter or radius of the reference gauge is measured by the reference gauge measuring part at a measuring point on a central axis of the reference gauge; a measuring part that measures the workpiece in a workpiece coordinate system set for the workpiece while the workpiece is fixed to the rotary table based on the displacement measured by the counter unit; a first transformer that transforms a measurement value measured by the measuring part in the workpiece coordinate system into the reference gauge coordinate system; a corrector that corrects by the correction function the measurement value transformed into the reference gauge coordinate system by the first transformer; and a second transformer that transforms the measurement value corrected by the corrector in the reference gauge coordinate system into the workpiece coordinate system. a probe that measures the workpiece; a movement mechanism that holds and moves the probe; a rotary table to which the workpiece is fixed and which rotates the workpiece relative to the probe; a counter unit that measures a displacement of the movement mechanism; a reference gauge measuring part that measures a diameter or radius of a reference gauge based on the displacement measured by the counter unit along an axial direction in a reference gauge coordinate system set for the reference gauge while the reference gauge is fixed to the rotary table, the reference gauge having a columnar shape or cylindrical shape and having a known diameter or radius; a correction function generating part that generates a correction function based on a difference between the diameter or radius measured by the reference gauge measuring part and the known diameter or radius, when the diameter or radius of the reference gauge is measured by the reference gauge measuring part at a measuring point on a central axis of the reference gauge; a measuring part that measures the workpiece in a workpiece coordinate system set for the workpiece while the workpiece is fixed to the rotary table based on the displacement measured by the counter unit; a first transformer that transforms a measurement value measured by the measuring part in the workpiece coordinate system into the reference gauge coordinate system; a corrector that corrects by the correction function the measurement value transformed into the reference gauge coordinate system by the first transformer; and a second transformer that transforms the measurement value corrected by the corrector in the reference gauge coordinate system into the workpiece coordinate system.