1. A rotary table device for a machine tool comprising:a main shaft that is rotatably supported with respect to a frame by a first bearing in an insertion hole formed in the frame;
a table that is secured to an end side of the main shaft, and on which a workpiece, which serves as an object to be processed, is mounted; and
a clamp piston that is provided so as to be movable in an axial direction of the main shaft in the insertion hole,
wherein the main shaft has a clamp surface that faces the table,
wherein a pressure chamber is defined by the frame and the clamp piston,
wherein the table is brought into a clamped state by friction force that is generated between the clamp piston and the clamp surface by causing the clamp piston to press-contact the clamp surface when an operating fluid is supplied to the pressure chamber,
wherein the rotary table device further comprises a second bearing that is provided separately from the first bearing, the second bearing being provided between the table and the frame so as to contact the table and the frame, and being provided so as to directly support the table with respect to the frame, and
wherein at least part of the second bearing is provided so as to be positioned within a range of existence of the pressure chamber in a radial direction of the main shaft.