Provided is a holder device that uses a pressure medium suitable for gripping a long and thin grasped object, the device eliminating need for a small-diameter machining for a device body and allowing use of a material suitable for sleeve deformation at a portion where a pressure chamber is formed. A holder device capable of deforming in a radial direction for fastening a grasped object 7 through a function of a pressure medium, includes a device body 2, a sleeve 3 disposed at a leading end of the device body 2 for gripping the grasped object 7, a pressure chamber 8 formed circumferentially in the sleeve 3, and a support portion 9 provided continuously from the device body 2 for forming the pressure chamber 8 together with the sleeve 3.