Abstract: A moving mechanism for a cylinder is provided, in which a projection and groove are engaged by relative movement different from that of a helicoid mechanism and movement of inner and outer cylinders relative to each other can be freely set. In the moving mechanism, a first helicoid thread is helically formed on the inner surface of an intermediate cylinder, a second helicoid thread that threadably engages with the first helicoid thread is helically formed on the outer surface of a movable cylinder, and the intermediate cylinder is rotated so the movable cylinder is moved relative to the intermediate cylinder. A projection is formed on the outer surface of the movable cylinder and a groove engageable with the projection is formed in the inner surface of the intermediate cylinder. In a range where the first and second helicoid threads threadably engage with each other upon relative movement of the movable cylinder, the groove is formed parallel to the first helicoid thread.