An apparatus for measuring a circularity deviation of a cylinder of an object intended to be integrally rotated about a rotation axis, the cylinder being eccentric as either intended or not with the rotation axis, the apparatus includes a measuring device, a motion controlling mechanism, and a circularity deviation calculating device. The measuring device (25) is adapted to measure a circumferential surface (K) of the cylinder at each measuring point "p" thereon in a three-point contact method. The motion controlling mechanism is configured to permit the measuring device (25) to be moved along a circumference (K) of the cylinder, which circumference lays on a cross section of the cylinder perpendicular to the rotation axis (W), in contact with the circumferential surface (K) of the cylinder, during rotation of the cylinder about the rotation axis (W). The circularity deviation calculating device is designed to calculate the circularity deviation of the cylinder, on the basis of a relative position "x" of the rotation axis relative to the apparatus for measuring the circularity deviation, a rotating angle φ of the cylinder about the rotation axis, and an output "y" of the measuring device.