In typical ultrasonic testing using Lamb wave, a narrow band burst wave is used to excite the Lamb wave to reduce the influence of dispersion and to excite a single mode wave. However, a narrowband signal has a long duration thus the spatial resolution is low. In this study, to image the flaw in a plate structure with high spatial resolution, the Lamb wave is excited by a broadband spike pulse, and dispersion compensation is used to improve spatial resolution. Lamb waves are transmitted and received by scanning the transmitter and receiver, and flaw is imaged by synthetic aperture focusing technique after applying dispersion compensation. Although the received raw waveform spreads in the time direction and becomes complicated, it is shown that the waveform can be compressed into a pulse with high spatial resolution by dispersion compensation. The spatial resolution of the flaw image can be improved by dispersion compensation, and it is also shown that flaw could be imaged even when multiple modes are propagated simultaneously.