An ultrasonic wave is sent from a transmission element to a test element to produce a plate wave in the test element, and the plate wave propagating through the test element is received by a reception element to thereby test the test element on the propagation route of the plate wave. The other probe that is the other reception element or transmission element is disposed between the transmission element and the reception element. A probe holding mechanism that has support legs contacting the surface of the test element and keeps constant an angle of the other probe with respect to the surface of the test element is allowed to support the other probe. And, the other probe is allowed to cross over in non-contact the propagation route of the plate wave extending from the transmission element to the reception element by means of support legs.