To provide a clamp device that can remove foreign matters on a work receiving surface prior to work clamping via a simple structure.

The clamp device comprises a work receiving part 2 having a work receiving surface 2a fear supporting a workpiece W placed thereon, a clamp part 11 capable of reciprocation toward and away from the work receiving surface 2a or between a clamping position and an unclamping position, a double-acting clamping air cylinder 13 for moving the clamp part 11 from the unclamping position to the clamping position by feeding air into a first working chamber 13a and also evacuating air from a second working chamber 13b and for moving the clamp part 11 to the unclamping position by feeding air into the second working chamber 13b and evacuating air from the first working chamber 13a, and an air blow pipe 17 with a base end connected to the first working chamber 13a via a quick release valve 16 and a tip end 17a opened toward the work receiving surface 2a.