Disclosed herein is a hard disk apparatus, including: a magnetic recording medium; a recording head adapted to record information on the magnetic recording medium; a semiconductor laser adapted to be controlled for light emission in a cycle of a recording clock to irradiate a light spot upon the magnetic recording medium to carry out thermal assistance in magnetic recording by the recording head; a laser driving circuit adapted to drive the semiconductor laser at a timing and with optical power in accordance with a light emission timing signal and a laser power controlling signal; and a controller adapted to set laser power in accordance with at least one of characteristics of the magnetic recording medium, semiconductor laser and recording head and output the laser power controlling signal to the laser driving circuit so that the laser power is adaptively varied.