A frictional resistance reduction apparatus for a ship, comprising: an air blowing chamber to be arranged in a hull of the ship; and an air supply pipe for supplying air into said air blowing chamber, wherein said air blowing chamber comprises: a front plate in which air blowing holes are formed through which the air can be blown out into outboard underwater from said air blowing chamber when arranged in the hull, wherein said air blowing holes are formed so that, when the said air blowing chamber is arranged in the hull, they are arranged in a direction from a bow section to a stern section in a ship side bow section of the hull or in a ship width direction in a bow front section of the hull; and a back plate arranged to oppose to said front plate; characterized in that a diffusion plate is provided to partition a chamber internal space as a space of said air blowing chamber into a first part on a side of said back plate and a second part on a side of said front plate, wherein said first part and said second part are connected with each other only below said diffusion plate, and wherein said air supply pipe is connected with said back plate such that the air is blown toward said diffusion plate. an air blowing chamber to be arranged in a hull of the ship; and an air supply pipe for supplying air into said air blowing chamber, wherein said air blowing chamber comprises: a front plate in which air blowing holes are formed through which the air can be blown out into outboard underwater from said air blowing chamber when arranged in the hull, wherein said air blowing holes are formed so that, when the said air blowing chamber is arranged in the hull, they are arranged in a direction from a bow section to a stern section in a ship side bow section of the hull or in a ship width direction in a bow front section of the hull; and a back plate arranged to oppose to said front plate; characterized in that a diffusion plate is provided to partition a chamber internal space as a space of said air blowing chamber into a first part on a side of said back plate and a second part on a side of said front plate, wherein said first part and said second part are connected with each other only below said diffusion plate, and wherein said air supply pipe is connected with said back plate such that the air is blown toward said diffusion plate. a front plate in which air blowing holes are formed through which the air can be blown out into outboard underwater from said air blowing chamber when arranged in the hull, wherein said air blowing holes are formed so that, when the said air blowing chamber is arranged in the hull, they are arranged in a direction from a bow section to a stern section in a ship side bow section of the hull or in a ship width direction in a bow front section of the hull; and a back plate arranged to oppose to said front plate; characterized in that a diffusion plate is provided to partition a chamber internal space as a space of said air blowing chamber into a first part on a side of said back plate and a second part on a side of said front plate, wherein said first part and said second part are connected with each other only below said diffusion plate, and wherein said air supply pipe is connected with said back plate such that the air is blown toward said diffusion plate.