A clamping device comprising: a distal end side stationary blocks which are provided on a side of a distal end of a workpiece retaining base, and in which stationary tilt faces tilting downwardly to a central direction of the workpiece are formed; a proximal end side stationary blocks which are provided on a side of a proximal end of the workpiece retaining base, and in which upward stationary tilt faces tilting downward toward the central direction of the workpiece are formed; and a movable block which is arranged at a position proximal to the proximal end side stationary blocks, and is capable of advancing to or retracting from a side of the distal end side stationary blocks with the workpiece being held between the blocks, and in which a downward movable tilt face tilting upwardly toward the central direction of the workpiece is formed.