In a process of braking an spindle motor, a frequency of a read clock signal synchronized with an RF signal output from an RF amplifier is measured as a first frequency by a braking control circuit. A brake is then applied to the spindle motor for a predetermined time. Thereafter, the frequency of the read clock signal is measured as a second frequency. Next, the braking time is calculated on the basis of: a frequency difference obtained by subtracting the second frequency from the first frequency; the first frequency; and a measuring time from the timing when the first frequency is measured to the timing when the second frequency is measured.