Impulsive force based on the collapse of cavitation is an important problem for fluid machinery. Collapsing behavior in the separated shear-layer cavitation is known to be high impulsive, so it is investigated using a contraction and divergence tunnel. The impulsive force at the collapse of cavitation is detected using an accelerometer. In addition, cavity behaviors are investigated in detail using a high-speed-video-camera triggered by the accelerometer. As a result, it is reported that two characteristic patterns of bubble collapse are observed in relation to cavitation impact.