The flashing reduces the part quality and the productivity of the molding process. We developed a contact pressure sensor to detect the flashing immediately. The performance of the sensor was analyzed in a simple 2D simulation. The sensor was applied to an automotive bumper mold with cavity pressure sensors. It showed sensitive output signal for the mold response by the cavity pressure change. It was confirmed that the flashing at the gate area occurred in the filling stage by the pressure increase due to growth of the melt flow length. The sensor output was correlated with the cavity pressure sensor output.