The phase interpolator includes two adjustable delays 30 and 31, phase comparator 32 which detects a phase difference between a signal delayed by the adjustable delay 30 and a signal delayed by the adjustable delay 31, an integrator 33 which integrates the outputs of the phase comparator 32 and multipliers 34-1 and 34-2 which set a control voltage for the adjustable delays 30 and 31. The feedback loop comprising phase comparator 32 and integrator 33 controls a delay amount of the adjustable delay 30 thereby securing a phase relation between {ACK1, ACK2} and ICK to achieve a stable ICK phase.