To downsize a whole chuck device and to strengthen force for holding a workpiece.

The chuck device 1 includes a chuck mechanism part 7 and a chuck drive part 9 for making the chuck mechanism part 7 open and close. The chuck drive part 9 includes: a casing 21; a first fluid chamber 27 and a second fluid chamber 31; a first piston 23 which forms one wall surface of the first fluid chamber 27; a second piston 25 which forms one wall surface of the second fluid chamber 31; a communicating passage 35 connecting the first fluid chamber 27 and the second fluid chamber 31; and internal fluid OL filled in the first fluid chamber 27, the second fluid chamber 31, and the communicating passage 35. The first piston 23 is arranged outside of the casing 21, being dislocated from the casing 21, and a projected area on the surface in contact with internal fluid OL of the second piston 25 is formed larger than a projected area on the surface in contact with internal fluid OL of the first piston 23. By applying pressure of supplied fluid AR to the first piston 23, the second piston 25 presses the chuck mechanism part 7.