To provide a wedge angle control device for automatically controlling the wedge angle with high accuracy to always keep an own ship's trim angle at the optimum trim angle.

This wedge angle control device controls the angle of a wedge rockably mounted at the ship's bottom of the stern to adjust the trim angle of an own ship by varying the inflow angle of flowing water. In the control device, according to the speed information on the own chip from a speed detecting part 10, the optimum trim angle θ* is computed using a map by an operating part 11, subsequently a deviation θ*-θ between the optimum trim angle θ* and the real trim angle θ of the own ship mentioned later is subtracted by a subtractor 12, and the wedge angle α is controlled to make the deviation θ*-θsmaller.