PURPOSE: To test a DUT speedily using an A/D circuit for an IC tester.

CONSTITUTION: A driver 3 feeds a test pattern to each input pin of a DUT 10 and an A/D circuit 4 receives the output of the DUT 10. A strobe judging circuit 5 receives the output of the A/D circuit 4 and judges the output result of the DUT 10. The A/D circuit 4 is provided with an A/D converter which receives the output of the DUT 10, an 'H' limit comparator and an 'L' limit comparator both of which receive the output of the A/D converter, an OR gate which receives the output of the 'H' limit comparator/'L' limit comparator, an FF which receives the output of the OR gate, an 'H' limit data memory, an 'L' limit data memory, and an interface circuit.