A storage apparatus of an embodiment includes a magnetic disk, a head, and a controller. The head includes a writing unit that outputs a magnetic field to record write data into a recording region of the magnetic disk to which light is irradiated and a reading unit that reads read data from the recording region of the magnetic disk. Based on a first spectrum of first read data read by the reading unit at a first position of the magnetic disk and a second spectrum of second read data read by the reading unit at a second position which is a following position of the first position, the controller detects whether an offset of the writing unit occurs while writing into the recording region of the magnetic disk is performed by the writing unit.