In wind tunnel studies on the flow around bluff bodies accompanying a large separated wake, the walls of the test section severely effect the flow characteristics around them. Proposed in this paper is a correction formula for the wall effects upon two-dimensional (2-D) unsteady separated flow of incompressible fluid around bluff bodies. The proposed formula is derived from numerical results with the discrete vortex method on 2-D separated flows around an inclined flat plate, a square cylinder, and also an elliptic cylinder located between two parallel walls. It is found that the present correction formula estimates reasonably well the wall effects upon the mean and fluctuating force coefficients over a wide range of blockage ratio and angle of attack through comparing the present calculated results with numerous experimental ones by several authors.