A delay circuit generates an internal clock signal or a second clock signal by delaying an external clock signal. A detection-potential generation circuit included in a phase-difference determination circuit generates a detection potential corresponding to a difference between a timing of an active edge of an internal clock signal or a third clock signal and a timing of the target external clock signal in a first node. A reference-potential generation circuit included in the phase-difference determination circuit generates a reference potential in a second node. A phase control circuit delays the second clock signal according to the detection potential. At this time, when the detection potential is higher than the reference potential, an adjustment amount of the second clock signal per adjustment changes.