To provide a grinding worm satisfying a requirement of a high-rigidity and precision and not exceeding a general replacement time in a small-size tool, and a tool securing system of other rotary tool.

Two clamp rings are provided for detachably installing a rotating machining tool (3) on a tool spindle (2) of a machining device, and particularly for installing a grinding wheel flange (4) on a spindle head (1) of a grinding spindle (2). A fastening pressure (F) formed by a fastening screw (7) is equally dispersed on a spindle flange (6) by clamp rings (10 and 13) attached in the shape of cardin. According to a tool installation of the present invention, a large-size tool can be replaced by short-time working, which is enlarged in weight and revolves at a high speed and is accompanied with a high requirement in the point of giving repeatability to a strength and run out in a radiation direction and an axial direction and a balance.