The cavitation characteristics were experimentally investigated about long circular-cylindrical orifices of various throat lengths including the orifice with a trip wire. Especially, the shedding process of separated vortex cavity was examined using high-speed photography. Cavitation impacts were measured with an accelerometer. As a result, it is found that the periodic shedding of a cloud-like cavity can be observed in the transition cavitation stage and is dependent on the formation and coalescence of micro-vortex cavities on the separated shear layer, as well as the reentrant motion after the shedding. It is also pointed out that it forms a feedback loop in the self-exciting mechanism. A good estimation using two velocity ratios can be made on the Strouhal number of a cloud-like cavity. The clear shedding of a cloud-like cavity appears near the cavitation impact-peak region and remains almost constant irrespective of the difference in orifice length.