Transmitted light through a diffuse scattering medium includes strongly diffused light (SDL) and weakly scattered light (WSL). To realize clear transillumination imaging through thick body tissue, which is typically more than 10 mm, we developed a technique to extract the WSL component from diffused light. A diffuser is placed on the incident surface of a scattering medium. We can extract the WSL component by subtracting the light intensity at the output surface with a diffuser from that without a diffuser. In CW measurements using a 15-mm-thick scattering medium (reduced scattering coefficient μs' = 1.0/mm), the spatial intensity distribution of the scattered light at the output surface was confined to an approximately 50% area by the proposed technique. It was confirmed in a time-resolved measurement that the earlier time component with a smaller temporal spread was extracted by the proposed technique.