Abstract: An excavator for excavating a tunnel is provided which has a body provided with gathering and transporting means for the materials excavated by the excavator for discharging the same. The excavator comprises a horizontally and vertically swingable boom mounted on the body and actuated by a cylinder-piston assembly interconnected between the body and the boom. A vertically tiltable excavating cutter is tiltably mounted on the forward end portion of the boom with or without a vertically swingable bracket actuated by a cylinder-piston assembly which is interposed between the cutter and the boom. An impact motor is adapted to intermittently actuating the cutter. An extensible and retractable boom actuated by a cylinder-piston assembly may be interposed between the bracket and the horizontally and vertically swingable boom.