A scrambler that facilitates encryption of data to be recorded and a magnetic storage device using this are provided. The scrambler has a shift register of a plurality of stages and an exclusive OR circuit that finds the exclusive OR of the logic of the stages of the shift register that correspond to a single generating polynomial. The output of the exclusive OR circuit is arranged to be fed back to the initial stage of the shift register. At least this single generating polynomial is an arbitrary generating polynomial. The drive number, in binary form, that identifies the storage device, is set as the initial value of the shift register of a plurality of stages.