Flyer acceleration experiments are carried out using a KrF laser system with a pulse duration of 10–15 ns and an intensity of ∼1.0 × 1013 W/cm2. Three-layered targets (aluminum–polyimide–tantalum) are used. First, an average velocity of laser-driven tantalum flyers with a thickness of 4 and 8 μm is estimated. Then, in a collision of a flyer with a copper layer attached to a diamond plate, we measure a transit time of a shock wave in the diamond. The impact velocity is estimated based on the transit time and a numerical simulation. This numerical simulation also shows that the initial peak pressure caused by the impact of a 4-μm-thick flyer is kept at 11 Mbar for 12–13 μm in thickness. Finally, whether this thickness is enough for EOS measurements is discussed.