A high-frequency treating instrument for an endoscope, includes: a spatula-form high-frequency electrode which is adapted to be protruded from and housed within an insulated flexible sheath of the endoscope; and a concavo-convex portion which serves as an antiskid member when the concavo-convex portion is brought into contact with a mucous membrane and is formed on at least one of side edge portions of a portion closer to a tip end of the high-frequency electrode.