An acoustic matching layer 1 according to the present invention includes a first acoustic matching layer 2, which has a low density and a low sonic velocity, and a second acoustic matching layer 3, which has a higher density and a higher sonic velocity. The first acoustic matching layer 2, of which the acoustic impedance is matched to that of a medium into an ultrasonic wave is radiated, is provided closer to the medium, while the second acoustic matching layer 3 is provided closer to a piezoelectric layer, thereby increasing the sensitivity of an ultrasonic transducer.