control section 110 judges whether the magnetic head has arrived at the sector before the certain number of sectors from the target sector by obtaining information on position of the magnetic head from the svc 116 then the process shifts to step s 108 in step s 108 the control section 110 supplies the current to the heater 126 h of the magnetic head based on the table specifically the control section 110 passes information of the current to be supplied to the heater control circuit 121 a at first then based on the information the heater control circuit 121 a supplies the current to the heater 126 h via the heater driver 121 h the process then shifts to step s 109 in step s 109 the control section 110 judges whether or not the magnetic head has arrived at the target sector by comparing information related to the request from the host unit stored in the ram 114 and the information on the position of the magnetic head obtained from the svc 116 when the magnetic head has arrived at the target sector the process shifts to step s 110 in step s 110 the control section 110 executes the read or write operation based on the information on the request from the host unit stored in the ram 114 then the process ends thus it is possible to expand the magnetic head in a sector whose error rate is high on the same track therefore it.