In a direct injection diesel engine, combustion characteristics are greatly influenced by the mixture formation behavior of the fuel spray. Diesel spray behavior depends on various conditions such as nozzle geometry, injection pressure, and ambient gas density. Boost pressure and exhaust gas recirculation ratio are set to increase for improvement of diesel engine performance. Consequently, compressed air density in an engine cylinder is becoming high due to high boost pressures, and it seems that the compressed high-density air affects the spray behavior more strongly. Therefore it is necessary to understand precise spray behavior under high ambient air density conditions. In this study, the behavior of diesel spray was visualized with shadow and tomographic imaging methods. Spray angles were obtained from shadow images, and the effect of high ambient pressure was investigated. For quantitative assessment of spray velocity, time-resolved particle image velocimetry was applied to sequential images of the diesel spray. The main results were as follows. Even under ultrahigh-boost pressure conditions, the relationship between ambient pressure and spray angle was shown with the modified empirical equation proposed by Hiroyasu and Arai [Trans. J. SAE, vol. 21, pp. 5-11, 1980]. Velocity distribution inside the spray corresponded to Goertler's distribution of the axisymmetric free jet; however, both velocity distributions of Tollmien and Goertler did not fit the spray velocity near the periphery of the spray.