The interface circuit includes n buffer circuits, switches for connecting an external pin of a tester to input nodes of n buffer circuits and connecting output nodes of n buffers respectively to n DUTs when a signal is provided from the tester to n DUTs, and successively connecting n DUTs to the external pin of the tester by a prescribed time period when voltage-ampere characteristics of n DUTs are measured. Therefore the number of devices that can be measured by the tester at a time can be increased by n times. As a result, the test cost can be reduced and the test accuracy can be improved.