An arc array slit is used for generating the focused Lamb wave by laser, where spatially expanded Nd:YAG pulse laser is illuminated through the arc array slit on the surface of a sample plate to generate the Lamb wave of the same pattern as the slit. Then the generated Lamb wave is focused at the focal point of which distance from the slit position is dependent on the curvature of slit arc. The focusing effect enables to acquire higher intensity of wave at the focus, better SNR in the received signal, and improved spatial resolution than when we use the conventional line array slit. This paper proposes a new imaging technique using this laser-generated focused Lamb-wave, which gives more accurate information about the size and the location of defects in thin plate. In order to verify the usefulness of the proposed method, experiments is carried out for the detection of the artificial linear and circular defects on a thin aluminum plate.