In this paper, authors conducted experimental investigations on cavitation damage to specimens of pure aluminum placed in a venturi type cavitation tunnel. The main object of experiments is to confirm the relation between damage intensity and flow velocity. Conclusions obtained are as follows; (1) Cavitation damage intensity is largely affected by flow velocity, for instance, the number of erosion pits varies with the 5 to 6 th power of flow velocity. (2) Erosion pits are generated near the end of fixed-cavity. (3) Distribution of erosion pits are supposed to be caused by difference of initial radius of a collapsing bubble and oscillatory variation of length of fixed-cavity. Simplified equation of bubble radius is also solved numerically and by the calculation of pressure field around a collapsing bubble, following results are obtained; (4) Maximum pressure on bubble wall varies with the 11 th power of flow velocity. (5) Maximum velocity of bubble wall varies with the 5 th power of flow velocity. (6) On the assumption that damage intensity increases in proportion to impulse provided to surface of specimens, these calculations show good agreement with experimental results.