FILTER CIRCUIT

PROBLEM TO BE SOLVED: To provide a technology for setting the cut-off frequency of a low-pass filter in a read-channel appropriately. SOLUTION: The filter circuit comprises a low-pass filter 14, a time- measuring circuit 15, a storage/operation circuit 19 and a current supply circuit 18 where the time measuring circuit 15 counts the number of pulses of reference clock, the storing/operating circuit 19 determines the average value of first and second set values corresponding to the current value of a control current when the number of pulses of reference clock increases by 1, and the current supply circuit 18 supplies a control current corresponding to the average value to the low-pass filter 14. Since a control current of the current quantity corresponding to a current set value can be supplied, even if the same number of pulses are counted a plural number of times by determining a desired current set value from the average value of first and second set values, cut-off frequency can be set finely, even if the frequency of reference clock is low, by setting the current value of control current finely.