Ultra-wide band (UWB) radar is capable of high range resolution near field sensing, and is thus applicable to security systems designed to identify a human body even when invisible. Although Synthetic Aperture Radar (SAR) creates a stable and accurate target image for such applications, it often suffers from increased shadow regions in the case of complex or multiple targets. On the contrary, a multiple scattered wave has the potential to enlarge a visible range on target surfaces because it propagates a path which differs from that of a single scattered wave. While various algorithms based on time-reversal processing with multiple scattered waves have been developed, these require a priori information of the surroundings or a target model. This paper proposes a shadow region imaging algorithm based on the aperture synthesis of multiple scattered waves. While the proposed algorithm only synthesizes a double scattered wave according to its propagation path, it can directly increase the visible area and is applicable to arbitrary target shapes. The results from the numerical simulation and experiment verify that the proposed algorithm directly makes a shadow region visible without a preliminary observation.