A method of and an apparatus for measuring the strength of ultrasonic waves are provided. They are capable of measuring the strength of ultrasonic waves easily and at low cost without using a sound pressure meter. The ultrasonic wave strength measuring apparatus has a particle source soaked in a cleaning liquid, an oscillator to generate the ultrasonic waves whose strength is going to be measured to vibrate the particle source so that particles are eluted from the particle source into the cleaning liquid, a counter to count the number of particles in the cleaning liquid, and an operation unit to find the strength of the applied ultrasonic waves based on the counted number of particles.