Abstract: A measuring instrument for measuring the contour of the outer surface of a workpiece. This measuring instrument is of such an arrangement that the tip end of a stylus solidly secured at one end of an arm adapted for rotational movement is brought into contact with the outer surface of the workpiece by a slight pressing force, the arm in this condition is moved in the axial direction thereof, and the displacement of the stylus tracing the irregularities of the outer surface of the workpiece to vertically move due to the abovedescribed movement is converted into the rotational movement of the arm, which is measured by measuring means such as a differential transformer, whereby the contour of the outer surface of the workpiece is measured from the vertical movement of the stylus and the axial (or horizontal) movement of the arm.