A fan device including: a casing unit having an axis (A) and including a casing body that is formed with a receiving space and an air outlet port in spatial communication with said receiving space , a porous plate that is formed with a plurality of through holes and that is disposed in said receiving space to divide said receiving space into an air-flowing room and a noise-reduction room aligned with and spaced apart from each other along the axis (A), and an air-entering tube that is connected to said casing body and that is in spatial communication with said air-flowing room ; and a fan impeller unit mounted in said casing unit , disposed in said air-flowing room of said receiving space and being rotatable about the axis (A) to generate airflow that partially flows from said air-flowing room into said noise-reduction room through said through holes of said porous plate ; characterized in that said casing body of said casing unit includes a base and a cover connected to said base to cooperatively define said receiving space , said base cooperating with said porous plate to define said noise-reduction room , said cover cooperating with said porous plate to define said air-flowing room , said porous plate being further formed with an inner tube-communicating through hole spaced apart from said through holes , said air-entering tube peripherally and outwardly extending from and in spatial communication with said inner tube-communicating through hole and extending out of said casing body to the external environment. a casing unit having an axis (A) and including a casing body that is formed with a receiving space and an air outlet port in spatial communication with said receiving space , a porous plate that is formed with a plurality of through holes and that is disposed in said receiving space to divide said receiving space into an air-flowing room and a noise-reduction room aligned with and spaced apart from each other along the axis (A), and an air-entering tube that is connected to said casing body and that is in spatial communication with said air-flowing room ; and a casing body that is formed with a receiving space and an air outlet port in spatial communication with said receiving space , a porous plate that is formed with a plurality of through holes and that is disposed in said receiving space to divide said receiving space into an air-flowing room and a noise-reduction room aligned with and spaced apart from each other along the axis (A), and an air-entering tube that is connected to said casing body and that is in spatial communication with said air-flowing room ; and a fan impeller unit mounted in said casing unit , disposed in said air-flowing room of said receiving space and being rotatable about the axis (A) to generate airflow that partially flows from said air-flowing room into said noise-reduction room through said through holes of said porous plate ; characterized in that said casing body of said casing unit includes a base and a cover connected to said base to cooperatively define said receiving space , said base cooperating with said porous plate to define said noise-reduction room , said cover cooperating with said porous plate to define said air-flowing room , said porous plate being further formed with an inner tube-communicating through hole spaced apart from said through holes , said air-entering tube peripherally and outwardly extending from and in spatial communication with said inner tube-communicating through hole and extending out of said casing body to the external environment. <EOS>