For the purpose of constructing the design rules of air-breathing laser launcher, the expansion of plasma, which was produced from air by focusing pulse laser, was investigated. A 1O-J-pulse TEA CO2 laser was used for these experiments. First, plasma was formed in a quiescent atmospheric air. Photographs and shadowgraphs were taken using an ICCD camera with high-speed gating. From the photographs, the propagation velocity along the laser axis was measured. The velocity was found around iO mIs much higher than that of a detonation wave calculated using LSD model. Since laser intensity at the plasma front was below the threshold for LSD regime, absorptionlexpansion mechanism other than LSD might predominate under the experimental condition. Shadowgraphs were taken to measure the expansion velocity of plasma and that of shock wave around plasma. The flow facility, in which plasma is formed in Mach 2 stream, was presented.