PURPOSE: To obtain a technology for ensuring the AC characteristics using an existing tester or an inexpensive tester even if the operating frequency and function of an LSI are enhanced.

CONSTITUTION: When the AC characteristics of an LSI are measured, signal from a control terminal 11 is set at 1 level. A control circuit 6 functions to establish a path from an input pin 3 through a critical path equivalent circuit 5 to an output pin 4. When a signal (of any frequency) varying from 1 to 0 (or from 0 to 1) is fed to the input pin 3, a signal appears at the output pin 4 while passing through the critical path equivalent circuit 5 with a time lag equivalent to the critical path of the circuit of actual product. Phase difference (time lag) between the signal appearing at the output pin 4 and the input signal is then measured and when the it is within an allowable range, the AC characteristics are satisfied and a decision is made that the LSI is acceptable.