To make ?Hydrogen vehicles and refueling station systems? fit for public use, research on hydrogen safetyand designing mitigative measures are significant. For compact storage, it is planned to store under highpressure (40MPa) at the refueling stations, so that the safety for the handling of high-pressurized hydrogenis essential. This paper describes the experimental investigation on the hypothetical dispersion and explosionof high-pressurized hydrogen gas which leaks through a large scale break in piping and blows down toatmosphere. At first, we investigated time history of distribution of gas concentration in order to comprehendthe behavior of the dispersion of high-pressurized hydrogen gas before explosion experiments. The explosion experiments were carried out with changing the time of ignition after the start of dispersion. Hydrogen gaswith the initial pressure of 40MPa was released through a nozzle of 10mm diameter. Through theseexperiments, it was clarified that the explosion power depends not only on the concentration and volume ofhydrogen/air pre-mixture, but also on the turbulence characteristics before ignition. To clarify the explosionmechanism, the numerical computer simulation about the same experimental conditions was performed. Theinitial conditions such as hydrogen distribution and turbulent characteristics were given by the results of theatmospheric diffusion simulation. By the verification of these experiments, the results of CFD were fully improved.