Patent ID: 7636646

Claim:
A roundness measuring device comprising: a rotation unit rotating a measured object around a rotation axis; a detector unit detecting a contact based on the contact of the detector unit with the measured object; and a measurement acquisition unit assuming a detection line connecting the rotation axis and the center of the detector unit when a contact is detected by the detector unit, obtaining a distance between the rotation axis and an intersection where the detection line intersects a surface of the detector unit as a measured distance, and obtaining a rotating angle provided by the rotation unit as a measured angle, and the roundness measuring device further comprising: an eccentric position calculation unit calculating, based on the measured distance and the measured angle, a distance between the axis of the measured object and the rotation axis as an eccentric distance, and calculating an angle formed between the detection line and a line segment connecting the rotation axis and the axis of the measured object as an eccentric angle; and a measurement correction unit correcting the measured distance based on the eccentric distance, the eccentric angle, the measured angle, a radius of the measured object, and a length from the center to the surface of the detector unit, and correcting the measured angle by adding a correction angle to the measured angle, the correction angle being formed between the detection line and a line segment connecting the rotation axis and a contact point where the measured object and the detector unit come in contact with one another.