One of the authors has made clear the bubble behaviors around the bubble collapsing period as well as the patterns of bubble collapse near solid wall through instantaneous measurement of an impulsive force and bubble appearance under a really flowing condition using a high speed video system composed of an impulsive force sensor and a high speed video camera. In this report, a simultaneous observation of bubble collapsing behavior and cavitation erosion pits is tried in separated vortex flow behind a circular cylinder to experimentally prove the ability of damage for the bubble collapsing patterns reported in the previous papers. As a result, the simultaneous observation of the bubble collapsing behavior and the erosion pits are successfully conducted with the present measurement system so that the damage ability is confirmed, at least, for a collapsing pattern of the axial collapse type, and the details of its collapsing behavior are also shown at the same time.