This study investigated nondestructive testing of welded steel plates by imaging ultrasonic wave propagation based on laser generation. The specimens were scanned by a pulsed laser, and the signals were received by a fixed piezoelectric transducer. A moving diagram of wave propagation from the fixed point was obtained directly from the collected signals. Wave scattering due to a weld defect (e.g., toe crack or root crack) was successfully imaged on weld specimens, and was easily recognized by visual observation in the measured moving diagrams. These experiments demonstrated the ability of the imaging technique to inspect a large area in a short time and to reliably detect a defect. Furthermore, the position-time-amplitude maps (B-scope images) were reconstructed from the moving diagram along some lines perpendicular to the defect, and the location and the size of a root crack were evaluated based on the B-scope images.