To provide a user-friendly clamp device capable of easily and accurately managing fastening force of a band despite a simple and inexpensive constitution.

The clamp device 1 has a strap band 3 and a support part 6 installed on one end side of the band 3 and rotatably supporting a screw element 5 threadedly engaged with a rack 4 provided on the other end side outer periphery of the band 3, and winds and fastens the band 3 by threadedly advancing the rack 4 threadedly engaging with the screw element 5 by rotating the screw element 5 in the winding-fastening direction. When fastening force of the band 3 becomes a predetermined value or more, a base end part 63 is deformed so that the tip side of the screw element 5 is rocked with the base end side of the screw element 5 as the rocking center by reaction to the screw element 5, and threaded engagement of the screw element 5 and the rack 4 is released, and afterwards, the tip side of the screw element 5 is rocked with the base end side of the screw element 5 as the rocking center, and deformation of a support part 63 is restored so that the screw element 5 and the race 4 are threadedly engaged with each other.