Abstract: A frequency tool for use in endoscopic electro-surgery, the high frequency tool having a high frequency knife at a distal end of a flexible cord encased in a tube member of a flexible sheath. A tubular rigid tip member of electrically insulating material is fitted in a fore distal end portion of the tube member, forming an annular flat end face together with the tube member. Formed internally of the tubular rigid tip member is a through axial passage hole to receive therein a retractably protrusible electrode member of the high frequency knife. At a fore distal end of a rod portion, the electrode member is provided with a spherically bulged portion of a diameter smaller than inside diameter of the axial passage hole of the tubular rigid tip member.