When a high pressure argon gas from 3 to 150 ata was irradiated by afocused XeCl excimer laser light with the maximum power of 15MW, a hot and dense plasma was produced. The dense plasma produced at the focal spot developed not only backward but also forward to the focal spot, which differed from one produced by visible laser light. The backward plasma length was calculated on basis of the breakdown wave and the radiation supported shock wave mechanisms, and agreed with the experimental one. At high pressures, the breakdown wave is dominant, while the radiation supported shock wave is predominant at low pressure. The backward plasma length produced by ultraviolet laser light was nearly equal to that produced by visible laser light. However, the total plasma length including the forward plasma length became to be about twice than that by visible laser light.