Abstract: An integrated circuit (IC) testing apparatus automatically detects and eliminates a phase difference between signals. A signal selection circuit 30 selects two test signals from a test pattern applied to a test device and outputs two test signals as a standard signal and comparison signal. A phase difference extraction circuit 40 extracts a phase difference between the standard signal and the comparison signal, while a mask circuit 50 generates a mask to eliminate unnecessary portions of the phase difference. A phase difference detection circuit 60 detects whether a phase difference exists and instructs whether to proceed with the counting of a counter circuit 90. A phase fail detection circuit 70 detects whether the phase of the comparison signal progresses ahead of the standard signal, and then outputs a fail signal. If a fail signal is not outputted, the counter circuit 90 determines the amount of delay of a programmable delay circuit 20 which then delays the comparison signal.