A treatment device for an endoscope, used for cutting body tissue, the treatment device being projectable from and retractable into an insertion tube of the endoscope, the treatment device comprising: a catheter (228; 230; 234) insertable into the insertion tube so as to be retractable into and projectable from the insertion tube, a control wire insertable into the catheter (228; 230; 234); and a cutting electrode (400; 410; 420; 430) mounted at the distal end of the control wire, the cutting electrode (400; 410; 420; 430) being formed in a bent hook-shaped configuration in advance, and the control wire being insertable into the catheter (228; 230; 234) to allow the cutting electrode (400; 410; 420; 430) being retractable into and projectable from a distal end of the catheter (228; 230; 234), wherein the cutting electrode (400; 410; 420; 430) is adapted to elastically deform in a state where the cutting electrode (400; 410; 420; 430) is retracted into the catheter (228; 230; 234), thereby assuming the shape the catheter (228; 230; 234), and the cutting electrode (400; 410; 420; 430) is adapted to recover the bent hook-shaped configuration in a state where the cutting electrode (400; 410; 420; 430) is projected from the catheter (228; 230; 234), characterized in that the treatment device further comprises a restraint instrument (50; 250; 234; 260) projetable from and retractable into the insertion tube, and adapted to restrain a leading end of the cutting electrode (400; 410; 420; 430), and the restraint instrument (50; 250; 234; 260) is adapted to restrain the leading end of the cutting electrode (400; 410; 420; 430) when the cutting electrode recovers the bent hook-shaped configuration when projected from the catheter (228; 230; 234). a catheter (228; 230; 234) insertable into the insertion tube so as to be retractable into and projectable from the insertion tube, a control wire insertable into the catheter (228; 230; 234); and a cutting electrode (400; 410; 420; 430) mounted at the distal end of the control wire, the cutting electrode (400; 410; 420; 430) being formed in a bent hook-shaped configuration in advance, and the control wire being insertable into the catheter (228; 230; 234) to allow the cutting electrode (400; 410; 420; 430) being retractable into and projectable from a distal end of the catheter (228; 230; 234), wherein the cutting electrode (400; 410; 420; 430) is adapted to elastically deform in a state where the cutting electrode (400; 410; 420; 430) is retracted into the catheter (228; 230; 234), thereby assuming the shape the catheter (228; 230; 234), and the cutting electrode (400; 410; 420; 430) is adapted to recover the bent hook-shaped configuration in a state where the cutting electrode (400; 410; 420; 430) is projected from the catheter (228; 230; 234), the treatment device further comprises a restraint instrument (50; 250; 234; 260) projetable from and retractable into the insertion tube, and adapted to restrain a leading end of the cutting electrode (400; 410; 420; 430), and the restraint instrument (50; 250; 234; 260) is adapted to restrain the leading end of the cutting electrode (400; 410; 420; 430) when the cutting electrode recovers the bent hook-shaped configuration when projected from the catheter (228; 230; 234).