Abstract: An AC test is disclosed which measures a time from the application of an input pulse on an input terminal of a circuit under consideration to the appearance of an output pulse on an output terminal of the circuit. The input terminal of the circuit is connected with an input driver through a first relay and connected with a pulse generator through a second relay. The opening-closing sequence of the first and second relays is selected such that the input terminal of the circuit is connected with at least one of the pulse generator and the input driver during a status setting of the circuit and during the application of the pulse. As a result, the occurrence of noises at the time of change-over operation between the pulse generator and the input driver is suppressed.