Abstract: An instrument for measuring ultrasound has a chamber through which sound waves can travel from end to end of the chamber. An acoustic focusing device near one end of the chamber concentrates the sound waves at a focal point near the opposite end of the chamber. A rotary shutter is supported within the chamber in a position to be rotated by passage of the concentrated sound waves. Devices capable of transmitting and receiving a ray of light are arranged on the instrument so that the light ray is interrupted by the rotary shutter to provide a series of light pulses. A counter is operatively connected to the light receiving device and the series of light pulses are utilized to actuate the counter and provide a reading indicative of the intensity of the sound waves. The instrument may have an additional indicator of the intensity of the sound waves to supplement the reading provided by the counter.