PURPOSE: To provide a steady rest device capable of concentrically holding a work independently of the diameter of the work.

CONSTITUTION: This device has a slide 3 capable of being moved in the center direction by the constant force, and two arms 1, 2 arranged opposite to each other, and holding devices 4-6 in each front end. The two arms 1, 2 are formed into the mirror symmetry in relation to the moving direction of the slide 3, and have cam surfaces 11, 12 for cooperating with surfaces of the cams 9, 10 of the slide so as to be turned around a turning connection part during the movement of the slide 3. When a work is not held, the holding devices 4, 6 are positioned at points separated from the center point in the radial direction at a distance smaller than the radius of the work to be held.