An ultrasonic wave propagating method capable of propagating plate waves between a probe and a test piece despite variations in the thickness or the surface angle of a test piece, and an ultrasonic propagating device and an ultrasonic testing device using this method. Ultrasonic waves are propagated between a probe (20) for transmitting or receiving ultrasonic waves and a test piece (100) for propagating plate waves. When propagating ultrasonic waves, a probe that can set an ultrasonic wave incident angle from the probe (20) to the test piece (100) and/or an ultrasonic wave receivable angle from the test piece to the probe in a plurality of states is used. A focal point type probe may be used as the above probe (20). When this type of a probe is used, it is oriented such that an oscillating direction axis L1 in the direction of which a reference axis along the propagation route of ultrasonic waves is oscillated around the focal point of the probe crosses the propagation element surface L2 including the test piece surface of a ultrasonic wave propagation element.