An ESD protection device is described, which includes a first P-type doped region, a second P-type doped region, a first N-type doped region, a second N-type doped region and an isolation structure. The bat body has a barrel section, a knob section, and a handle section. Preferably, the robot arm is in common with an arm used to move the patient in traditional proton therapy. A first projecting portion projects radially outwardly from an outer circumferential surface of the first cylindrical portion with a predetermined projecting amount.