PURPOSE: To accurately measure an impulse wave pressure by a method wherein a plurality of optical waveguides are intersected in part to be united with each other to form a pressure-receiving connection section and an intensity of a light, which leaks out from one of the waveguide to the other in accordance with a pressure applied on the pressure-receiving connection section, is measured.

CONSTITUTION: An impulse wave generating source of an apparatus such as an external body impulse wave calculus crushing apparatus or the like is disposed on an upper portion of a water tank. At an intersection part of an outputting and a receiving sides of optical fibers 11, 12, both of them are united with each other so as to be intersected in part to form a pressure-receiving connection section 14. A hydrophone 10 for measuring an ultrasonic wave is disposed so that the connection section 14 is on a focusing position of the impulse wave from the impulse generating source. An output terminal of a measuring section 30 is connected to a synchroscope. A light having a prescribed intensity level is emitted from an outputting section 20 to a receiving side of an optical fiber 11 via an optical fiber cable 40. A part of the light leaks to the optical fiber 12 via the connection section 14. The leaked light is inputted to a photodetector 31 of the measuring section 30 via an optical fiber cable 41 so that the optical intensity as measured.