In order to investigate gravitational instability induced by supersonic collisions between small, dense clouds and large, diffuse clouds, we perform the numerical hydrodynamic calculation by SPH code. We show that the large cloud is disrupted by the bow shock induced by the small cloud, and the small cloud is compressed. Final fates of the small cloud are divided into two cases. The first case is that the small cloud is ablated by the ram-pressure of the large cloud and is finally destroyed. The second case is that the central part of the small cloud left from the ablation gravitationally collapses. We discuss the condition dividing these two cases. Our condition show that even if the Mach number of collision velocity is very high, the small cloud can collapse.