To provide a clamping device of a workpiece rotating and supporting device facilitating manually moving of a clamping body and holding of a workpiece at low cost.

This clamping device of a workpiece rotating and supporting device includes a rotating and holding body rotatably supported by a support body and having a guide space part capable of guiding the workpiece and a clamping device 9 for clamping the workpiece. The clamping device is constituted of a shaft body 21 for clamping which has a distal end part which can be made to abut on the workpiece and has a male screw part and a groove part 22 formed on an outer periphery and in an axial center direction, respectively, a cylindrical guide body 15 which is provided in the rotating and holding body, is formed with a through-hole part 16 along a clamping direction and guides the shaft body 21 for clamping by projecting a distal end of a bolt 18 for regulating rotation into the groove part 22 from an inner periphery, and a cylindrical pressing body 31 spirally fitted to the shaft body 21. By moving the shaft body 21 to the workpiece side and rotating the cylindrical pressing body 15, the workpiece is clamped by pressing the distal end of the shaft body 21 on the workpiece side by making an end face of the cylindrical guide body 15 as a support surface.