PURPOSE: To check intermittent abnormalities quickly by making multiple sampling in one cycle of decision results of tested logical signals.

CONSTITUTION: A tested logic circuit 12 transfers determined output from a tester control circuit 15 to a check circuit 13 in response to a special pattern. In the circuit 13 a comparison circuit 31 compares tested signals with a threshold value by the level, supplies test signals to a decision circuit 32. The coincidence of the logical level with an expected value pattern is decided and the decision outputs are written in a fail memory 33 one after another by use of a multiple sampling clock.