Cylindricity measuring instrument is benchmark against precision rotary center and linear motion guide,the quantitative evaluation of the cylindricity is made by measuring the radius variation of actual contour of several cylindricity surface in different angle position to rotary center by displacement sensor in the guide. It is used to measure the error of contour shape of cylindricity workpiece (Roundness, cylindricity, planeness, straightness),position error ( concentricity, coaxiality, run-out and perpendicularity)