When the Reynolds number is larger than the critical value or laminar separation is eliminated by a trip installed on a hemispherical cylindrical body, attached spot cavitation is observed occasionally. It occurs at fixed place in the vicinity of the minimum mean pressure and grows into a triangular wedge. In the present investigation, isolated and parallel spot cavitation is artificially generated on a hemispherical body and the behavior of the cavitation is observed by using high-speed movies and instantaneous photographs. The frequency of damaging blows in the range of the flow speed of 25 to 50 m/s is obtained by counting the number of pits on an aluminum specimen. When spot cavitation occurs adjacently, the cavities become rather stable. The pitting rate at the maximum damage zone by the parallel spot cavitation is much smaller than that by the isolated spot cavitation. The total pitting rats at the maximum damage zone by the isolated and parallel spot cavitation vary roughly 5th power of the flow speed for the both cases.