In this article we are interested in the propagation speed for solution of hyperbolic boundary value problem in the WR class. Using the Holm- gren principle, we show that this speed is finite and we are able to give an explicit expression for the maximal speed. Due to propagation phe- nomenon along the boundary specific to the W R class, the maximal speed can be larger than the propagation speed for the Cauchy problem. This is consistent with examples of the litterature.