PROBLEM TO BE SOLVED: To easily release the engagement of a male screw part and a female screw part of a shaft body in a clamp device.SOLUTION: A clamp device according to one side face of this invention comprises: a shaft body formed with a male screw part which is engaged with a support mechanism a first operation member for rotating the shaft body around a shaft and an engagement release mechanism which releases an engagement state of the support mechanism and the shaft body. The support mechanism includes a plurality of female screw members which are engaged with the male screw part of the shaft body, and a plurality of elastic members which press the female screw members to the male screw part of the shaft body. The engagement release mechanism includes a plurality of engagement release members, and a second operation member which imparts forces to the engagement release members to a direction in which the female screw members are pressed. Each female screw member is constituted so as to be capable of taking a first position which is pressed by the elastic member and engaged with the male screw part, and a second position which separates from the male screw part by being pressed by the engagement release member while withstanding an elastic force of the elastic member.
