This paper describes the experimental and numerical results of a 45 deg. sweptback hydrofoil of NACA 0012 section and aspect ratio of 3, comparing them with those of an elliptical planform hydrofoil described in previous papers. In the experiment, lift and drag coefficients, pressure distribution of the hydrofoil, velocity distribution around tip vortex and wake distribution were measured at some typical conditions. Flow field around the foil was also investigated by the numerical computation. Following conclusions were obtained; (1) Pressure gradient from root to tip appears on the back side of the sweptback foil because of its planform configuration. This causes an out-flow in the boundary layer. (2) The sweptback foil is less prone to stall, compared to the elliptical foil. (3) The tip vortex cavity of the sweptback foil is weaker than that of the elliptical foil. The sheet cavity on the sweptback foil is divided into several parts which rotated at their terminations in the same direction as the tip vortex. These results can be elucidated by the occurence of longitudinal vorticity due to the out-flow.