A gripper comprising: a body case having, at one end, a cylinder part having a cylinder chamber which houses a piston so as to slide the piston along a central axis of the piston, and having, at the other end, a plurality of guide parts formed at regular intervals around the center axis and extending in a direction orthogonal to the center axis; a plurality of master jaws, on which top jaws can be removably mounted, guided by each of the guide parts; and a plunger having a plurality of interconnecting means which are respectively interconnected with each of the master jaws and slides along the central axis associated with a sliding operation of the piston, wherein: the gripper is configured such that each of the interconnecting means moves, by a sliding operation of the plunger, each of the master jaws in either direction along each of the guide parts, so as to cause each of the top jaws to grip a workpiece or to release the gripped workpiece; the body case has a first case which is provided on one side of the central axis and formed so that the cylinder chamber opens to the other side of the central axis, and a second case which is provided on the other side of the central axis and has each of the guide parts; the second case is fixed to the first case so as to cover an opening of the first case on a side of the second case; and each of the guide parts of the second case is provided with a projection projecting on an outer side of an outer peripheral surface of the cylinder part, and characterised in that screw holes for mounting the body case to a fitting body are provided in a first case side of the projections. a body case having, at one end, a cylinder part having a cylinder chamber which houses a piston so as to slide the piston along a central axis of the piston, and having, at the other end, a plurality of guide parts formed at regular intervals around the center axis and extending in a direction orthogonal to the center axis; a plurality of master jaws, on which top jaws can be removably mounted, guided by each of the guide parts; and a plunger having a plurality of interconnecting means which are respectively interconnected with each of the master jaws and slides along the central axis associated with a sliding operation of the piston, wherein: the gripper is configured such that each of the interconnecting means moves, by a sliding operation of the plunger, each of the master jaws in either direction along each of the guide parts, so as to cause each of the top jaws to grip a workpiece or to release the gripped workpiece; the body case has a first case which is provided on one side of the central axis and formed so that the cylinder chamber opens to the other side of the central axis, and a second case which is provided on the other side of the central axis and has each of the guide parts; the second case is fixed to the first case so as to cover an opening of the first case on a side of the second case; and each of the guide parts of the second case is provided with a projection projecting on an outer side of an outer peripheral surface of the cylinder part, and characterised in that screw holes for mounting the body case to a fitting body are provided in a first case side of the projections. the gripper is configured such that each of the interconnecting means moves, by a sliding operation of the plunger, each of the master jaws in either direction along each of the guide parts, so as to cause each of the top jaws to grip a workpiece or to release the gripped workpiece; the body case has a first case which is provided on one side of the central axis and formed so that the cylinder chamber opens to the other side of the central axis, and a second case which is provided on the other side of the central axis and has each of the guide parts; the second case is fixed to the first case so as to cover an opening of the first case on a side of the second case; and each of the guide parts of the second case is provided with a projection projecting on an outer side of an outer peripheral surface of the cylinder part, and characterised in that screw holes for mounting the body case to a fitting body are provided in a first case side of the projections.