A measuring probe for measuring a screw groove of a relatively rotatable ball screw includes a stylus having a tip end portion configured to contact the screw groove, a radial-direction displacement mechanism configured to support the stylus so as for the stylus to be displaceable in an X direction toward an axial center of the ball screw, an axial-direction displacement mechanism configured to support the stylus so as for the stylus to be displaceable in an axial direction (Z direction) of the axial center, and sensors configured to detect displacement of the stylus produced by the radial-direction displacement mechanism and the axial-direction displacement mechanism. This enables high-accuracy measurement of a predetermined position of a side surface of a relatively rotatable work.