Bentonite is considered as a buffer material for geological disposal because of its low water permeability and its ion exchange property. Understanding the behavior of groundwater inside bentonite is important to evaluate the radionuclides transfer for long-term safety, and a measurement system for water content in bentonite without destruction is required. Therefore, non-destructive measurement method using ultrasonic technique is focused on. In this study, transmitted waves of bentonite specimen with differential water content area were measured by two-dimensional scanning of laser vibrometer, and two-dimensional distribution of ultrasonic transit time of the bentonite specimen were obtained. As a result, ultrasonic diffraction through differential water content area was observed. Altogether, ultrasonic measurement for bentonite was validated.