a disk configured to store data;

a head configured to read/write data from/to the disk;

a first actuator configured to move an entire arm having the head disposed at a distal end;

a second actuator that is provided at the distal end of the arm and moves the head;

a first controller configured to control the first actuator according to a target position of the head at a multi-rate that is a 1/N cycle (N: an integer of 2 or more) of a head position observation cycle;

a second controller configured to control the second actuator according to the target position of the head at the 1/N cycle; and

a first additional filter that is added between the first controller and the first actuator and outputs output data to the first actuator according to input data from the first controller,

the method comprising:

by an arithmetic operation unit, measuring a head position error spectrum and a frequency characteristic by individually adding a test signal to an operation amount of the first actuator and an operation amount of the second actuator at the 1/N cycle in a state before the first additional filter is added, calculating a multi-rate sensitivity characteristic based on the frequency characteristic, and specifying a frequency to be corrected by the first additional filter based on the head position error spectrum and the multi-rate sensitivity characteristic; and

by the arithmetic operation unit, measuring, with respect to the frequency, a frequency characteristic by individually adding the test signal at the 1/N cycle to the operation amount of the first actuator and the operation amount of the second actuator in a state in which each of a plurality of candidates of the first additional filter is added, calculating a multi-rate sensitivity characteristic based on the frequency characteristic, and determining, as the first additional filter to be used, a candidate in which a peak of the multi-rate sensitivity characteristic is equal to or less than a threshold value and a head position error is minimized.