It is an object of the present invention to provide a magnetic recording medium which has a high level of magnetic anisotropy energy, retains stably the state of recording magnetization within the operating temperature range and is suitable for high-density recording with a low noise level, and a magnetic storage device for the magnetic recording medium. For attaining the above object, the magnetic recording film of the magnetic recording medium is characterized in that its magnetic anisotropy energy constant Ku at an absolute temperature of 300K is greater than 3.6null106 erg/cc and the average particle diameter is larger than 5 nm and smaller than 12 nm.