Abstract: Disclosed is a method of detecting bubbles issuing from a hermetic container. A hermetic container, i.e., an object to be measured, is immersed in a liquid, and pressurized air is applied to this hermetic container to produce bubbles from a leaking portion. The bubbles are allowed to pass between a pair of optical fibers provided with a gap therebetween. At that time, a light beam emitted from one optical fiber and received by the other optical fiber is radiated across the intended pathway of the bubbles. When the light beam passes through the bubbles, the beam is diffused by the difference in density between the liquid and the bubbles, a reduced part of it is received by the other optical fiber, and the amount of light thus received is converted to an electrical signal. In addition, an apparatus for detecting bubbles for implementing this method is also disclosed.