Unsteady cavitating flow around a flat plate hydrofoil was studied in order to investigate the effect of tip leakage vortex cavitation on the unsteady character of the cavitating flow. A two-dimensional flat plate hydrofoil having rounded leading and trailing edges with/without a tip clearance was tested for several angles of attack. The cavitating flow was filmed from the top and the side simultaneously using two high speed video cameras, and the unsteady static pressures just upstream and downstream of the hydrofoil were also simultaneously measured with the high speed video camera recording. It was found that, with the tip clearance, the partial cavity at the same cavitation number became more or less shorter and thinner than that without the tip clearance. Even under the existence of the tip leakage vortex cavity, the Strouhal number rule of the unsteady cavitating flow based on the attached cavity length still stood in our experiments.