To provide an ultrasonic vibrator reduced in the number of unnecessary vibration components and having a wide band frequency characteristics.

In an ultrasonic vibrator, a large-sized vibrator T having a radiation surface with a large area is formed by arranging a large number of small-sized vibrators t1, t2, t3... each having a radiation surface with a small area to push up an unnecessary radial vibration mode to a high-pass region and the thicknesses of the small-sized vibrators t1, t2, t3... are changed at random in the arranging direction of these vibrators at least at the center part of the large-sized vibrator T to expand a frequency band without exerting effect on the directionality of radiation.