Air-coupled ultrasonic testing device and air-coupled ultrasonic testing method

An air-coupled ultrasonic testing device is provided with a vertical ultrasonic wave transmitting element that transmits the vertical ultrasonic waves in the open tube resonance frequency band, which includes the center frequency (f) satisfying the condition of f≒Ｖ·Ｎ/(2t) (where N is a positive integer) when the thickness of the object under test of a multi-layered structure is t and the speed of sound of the vertical ultrasonic waves propagated by the object under test is V, towards the measurement point on the object under test placed in an air atmosphere; and a vertical ultrasonic wave receiving element that receives the vertical ultrasonic waves passing through the object under test.