A high-density sound-absorbing composite material is made from polyester. The sound-absorbing composite material is comprised of a porous sound-absorbing base material which is based on composite polyester fiber materials and having a density of from 150 kg/D to 350 kg/D and a synthetic resin sheet that is attached to one side of the base material. In addition, an apparatus is provided for producing a high-density sound-absorbing composite material made from polyester, wherein by using the apparatus, a synthetic resin sheet is adhered to the high-density and porous sound-absorbing base material which is based on composite polyester fiber materials. The apparatus is characterized by mechanisms for: (1) inserting sound-absorbing base materials between on a flat working board and under the sheet while the revolution speed of a supporting roller on which the sheet is wound is being controlled, (2) fixing both corners of the sheet by pulling them to make the sheet align with the edge of the sound-absorbing base material, and (3) adhering the sheet tightly to the sound-absorbing base material by rotational motion of the roller. As a result, by blocking air flow through a wall face while maintaining porosity for soundproofing (sound-absorbing) effect of a sound-absorbing plate, an adsorption by dust, etc. can be prevented.