Experiments were performed on the interaction between the reflected oblique shock wave and the separation shock wave ahead of the forward-facing step through the turbulent boundary layer. The turbulent boundary layer disturbed by the oblique shock reflection recovered exponentially in the downstream direction when the step was absent. The interaction was divided into three types according to the position of the step : (I) the reflection of the oblique shock is independent of the separation shock, (II) the recovery of the boundary layer is insufficient, and the separation shock becomes weak and merges with the reflected shock, (III) the new separation shock ahead of the incident shock plays the role of the reflected shock wave. These type were characterized by the shape factor of the boundary layer.