Abstract: An excellent rotary body measuring device is provided which is capable of properly observing and measuring a desired position of a rotary body in a rotating state from a required direction with use of a simplified device structure.

Abstract: Provided is a tool which is capable of precisely measuring a distance from a reference point such as a mechanical origin to a cutting edge, even where the cutting edge is small in diameter, thereby allowing the cutting edge to be precisely moved to a machining origin which is a machining start position. Targets (12), (13) are provided at a site displaced from a cutting edge (11) which is a machining site to a thicker base side, on the tool designated by numeral (1), for applying machining to a work piece (W). These targets are formed in an irregular shape for acting measuring mediums (Zy), (Zx) such as a probe or an electrode for contact-type measurement, light for optical measurement, or a sonic wave for displacement-type measurement, and further, light required for optical magnification-type stereoscopic vision or optical imaging.