A gas fire-extinguishing apparatus, comprising: an ejection head 13 having a nozzle section 12 which ejects high-pressure fire-extinguishing gas to a space; a conduit pipe 14 which is connected to the ejection head 13 and guides high-pressure fire-extinguishing gas to the ejection head 13; a fire-extinguishing gas supply source which supplies the high-pressure fire-extinguishing gas to the conduit pipe 14; and a silencer 17f which is disposed on the ejection head 13 and attenuates sound caused by ejection of the fire-extinguishing gas from the nozzle section 12, wherein the silencer 17f comprises a casing 129 comprising a cylindrical peripheral wall 121, an annular end wall 122 formed at one end in an axial direction of the peripheral wall 121 to be perpendicular to an axis of the peripheral wall 121, and a mounting section 123 detachably mounted on the ejection head 13; and a sound absorption material 125 which is accommodated in an inner space defined by the peripheral wall 121, the end wall 122 and the ejection head 13, and made of a porous metal, wherein: the sound absorption material 125 is formed in a columnar shape and an outer peripheral surface of which is formed in a cylindrical shape, an inner peripheral portion of the mounting section 123 includes a screw thread and an outer peripheral portion of the nozzle section 12 includes a corresponding screw thread, an end surface of one side 125b of the sound absorption material 125 in a direction of an axis of the sound absorption material 125 and an end surface 125c of the other side are formed on imaginary planes perpendicular to the axis of the sound absorbing material, the end surface 125b of one side and the end wall 122 are surface-contacted with each other; and the end surface 125c of the other side and the end surface of the nozzle section 12 are surface-contacted with each other by screwing the screw thread in the outer peripheral portion of the nozzle section 12 to the screw thread in the inner peripheral portion of the mounting section 123. an ejection head 13 having a nozzle section 12 which ejects high-pressure fire-extinguishing gas to a space; a conduit pipe 14 which is connected to the ejection head 13 and guides high-pressure fire-extinguishing gas to the ejection head 13; a fire-extinguishing gas supply source which supplies the high-pressure fire-extinguishing gas to the conduit pipe 14; and a silencer 17f which is disposed on the ejection head 13 and attenuates sound caused by ejection of the fire-extinguishing gas from the nozzle section 12, wherein the silencer 17f comprises a casing 129 comprising a cylindrical peripheral wall 121, an annular end wall 122 formed at one end in an axial direction of the peripheral wall 121 to be perpendicular to an axis of the peripheral wall 121, and a mounting section 123 detachably mounted on the ejection head 13; and a sound absorption material 125 which is accommodated in an inner space defined by the peripheral wall 121, the end wall 122 and the ejection head 13, and made of a porous metal, wherein: the sound absorption material 125 is formed in a columnar shape and an outer peripheral surface of which is formed in a cylindrical shape, an inner peripheral portion of the mounting section 123 includes a screw thread and an outer peripheral portion of the nozzle section 12 includes a corresponding screw thread, an end surface of one side 125b of the sound absorption material 125 in a direction of an axis of the sound absorption material 125 and an end surface 125c of the other side are formed on imaginary planes perpendicular to the axis of the sound absorbing material, the end surface 125b of one side and the end wall 122 are surface-contacted with each other; and the end surface 125c of the other side and the end surface of the nozzle section 12 are surface-contacted with each other by screwing the screw thread in the outer peripheral portion of the nozzle section 12 to the screw thread in the inner peripheral portion of the mounting section 123. the sound absorption material 125 is formed in a columnar shape and an outer peripheral surface of which is formed in a cylindrical shape, an inner peripheral portion of the mounting section 123 includes a screw thread and an outer peripheral portion of the nozzle section 12 includes a corresponding screw thread, an end surface of one side 125b of the sound absorption material 125 in a direction of an axis of the sound absorption material 125 and an end surface 125c of the other side are formed on imaginary planes perpendicular to the axis of the sound absorbing material, the end surface 125b of one side and the end wall 122 are surface-contacted with each other; and the end surface 125c of the other side and the end surface of the nozzle section 12 are surface-contacted with each other by screwing the screw thread in the outer peripheral portion of the nozzle section 12 to the screw thread in the inner peripheral portion of the mounting section 123.