Rotary movement converting mechanism and measuring instrument

A rotary movement converting mechanism for converting a rotary movement of a rotary body (43) into a linear movement of a movable body (2) has a support body (42) fixed to a body frame (3) and provided with a slit (42A) along an axial direction of the rotary body (43), a spiral groove (43A) formed on the inner circumference of the rotary body (43), and a top member (41) provided on the movable body (2). The top member (41) has an engaging member (41A) inserted through the slit (42A) and having a tip end engaged with the spiral groove (43A), and a stop member (41C) for stopping the linear movement of the movable body (2) when a load is applied on the linear movement of the movable body (2). Accordingly, when a load is applied on the linear movement of the movable body (2), the linear movement is stopped and the minute displacement of the movable body (2) is restrained, thereby enhancing the stability of a measuring instrument in measuring a workpiece.