PURPOSE: To reduce the sound propagation of high frequency to the surrounding by a percussion type drilling device which is excellent in sound-proofing performance.

CONSTITUTION: The outside of a guide cell 22 of a device main body 7 of a percussion type drilling device 1 is enveloped with a soundproofing cover which comprises a lining material of an aluminum-made outer plate, a lining material of a vinyl chloride sheet and an urethane foam-made core material, thereby preventing the percussion noise accompanied by hammering of a hammer drifter 24 against a drill lamb to a surrounding area. A soundproofing cover 12 is used to prevent the propagation of generated high frequency noise accompanied by hammering of the hammer drifter 24 against the drill ram to the surrounding area. This constitution prevents noise trouble and allows the percussion type drilling operation to be exerted to a satisfactory extent so that its originally designed advantage may be displayed.