This study reports an adaptation of acoustic sensing to detection of shellfish in the sediment. In this paper, we tried to detect Ruditapes philippinarum called asari in Japanese using a 1-MHz acoustic focus probe. Then, 2-D acoustic imaging of the shellfish in the sediment was performed, and the strong backscatter from the shell surface was detectable. Acoustic imaging was performed at some incident angles (0 degrees, 15 degrees, and 30 degrees) to decrease back scatter from the sediment and increase that from the shellfish. The result shows acoustic imaging at 30 degrees incident angle was the most efficient. Furthermore, weak scatter inside shell was also observed as good indicator for asari detection. In addition to the experiments, finite-difference time-domain (FDTD) simulation was performed to understand complex wave propagation generated by the focus probe. This simulation helped us to understand the experimental data.