According to one embodiment, a magnetic disk device includes a magnetic disk, a motor, a magnetic head, and a controller. A first area, and a second area located on an inner diameter side of the first area are provided in the magnetic disk. The motor rotates the magnetic disk. The controller receives a write command. In a case where a first position that is a position designated as a write destination of data by the write command is included in the first area, the controller writes the data to the first position by the magnetic head while rotating the magnetic disk at a rotational speed of a first value. In a case where the first position is included in the second area, the controller writes the data to the first position by the magnetic head while rotating the magnetic disk at a rotational speed of a second value larger than the first value.