Provided are an ultrasonic transducer, an ultrasonic probe, and an ultrasonic diagnostic device which enable an ultrasonic beam in the depth direction of diagnosis to be narrowly focused in a wide region, thereby obtaining a high-resolution diagnostic image. An ultrasonic transducer (100) is provided with an ultrasonic vibrator (110), a shape change layer (120) which is provided on the subject side of the ultrasonic vibrator and the shape of which is changed by an electrical signal, electrodes (141, 142) which are respectively disposed on both surfaces of the shape change layer (120), and a variable power source (140) which applies the electrical signal between the electrodes (141, 142), wherein the variable power source (140) varies the focus or diffusion of the ultrasonic beam by changing the shape of the shape change layer (120) by controlling the electrical signal to be applied between the electrodes (141, 142).
