PURPOSE: To simultaneously and efficiently measure the different kinds of ICs by providing the IC tester with a mask memory for storing mask information for masking defective information in a fail register in each item correspondingly to each IC.

CONSTITUTION: The IC tester is provided with the mask memory 22 for storing mask information M1 to Mn for masking defective information in the fail register in each item correspondingly to each IC 1. When a different sort of an IC is used even if a certain IC corresponding to a certain test item is decided as a defective one, AND between the defective information in the fail register and the mask information in the mask memory 22 is regarded as a defective signal. When mask information is applied to the IC decided as a defective one in a certain test item, the next test item is processed without accepting a defective signal corresponding to the test item concerned. Since an IC which does not require a certain test item can skip the test item, different sorts of ICs can be simultaneously measured.