One of differential signals is inputted to a first input terminal. The other of the differential signals is inputted to a second input terminal. A first sample hold circuit samples the signal inputted to the first input terminal and hold it thereafter. A second sample hold circuit samples the signal inputted to the second input terminal and holds it thereafter. A comparison unit compares a signal corresponding to a difference between respective output signals from the first and the second sample hold circuits, with a predetermined threshold value. A latch circuit latches an output from the comparison unit. Sample timings of the first and the second sample hold circuits and a latch timing of the latch circuit can be adjusted independently.