Embodiments of the present invention help to suppress the effects of thermal fluctuation in a thermally assisted magnetic field recording, and improve recording density. According to one embodiment, a recording area of a magnetic disk is heated and the full width at half maximum of an optical power distribution of a near field light generator is controlled to be 100 nm or less. Thereby, the cooling time of the magnetic disk is made 2 nm or less and the effects of thermal fluctuation are suppressed. Moreover, although an incomplete area of the magnetization reversal at the rear end of the magnetic domain is created with rapid cooling, by creating an overshoot at the rising end of the magnetic field waveform of the magnetic recording head, the incomplete area of the magnetization reversal can be overwritten, which is created at the rear end of the magnetic domain previously recorded by the overshoot magnetic field. Therefore, the expansion of the magnetic transition width can be suppressed, resulting in the recording density being improved.