An interface apparatus for a semiconductor integrated circuit and an interfacing method thereof controls the VOX of differential signals to a target level in response to the differential signals being outputted by an output block. The interface apparatus for a semiconductor integrated circuit includes an output block configured to output differential signals output by an internal circuit a detector configured to detect a timing error of the differential signals; and a controller configured to control a timing of the differential signals output by the internal circuit according to a detection result of the detector.