In this study, a hydrogen leak simulation apparatus was made, and then hydrogen diffusion behavior in the ground and in the atmosphere was measured, in order to clarify how to detect leaked hydrogen or respond after the leakage. The hydrogen leak simulation apparatus was composed of an underground simulation tank of 7 m in diameter and 1.35 m in depth, and an atmospheric simulation tank of 8 m wide x 8 m depth x 3 m height. The pipe was set in the underground simulation tank at the burial depth 1.2 m. A pinhole of 1 mm in diameter was made on the buried pipe, and the diffusion behavior of hydrogen gas released from the pinhole was measured. For the diffusion behavior in the ground, the concentration distribution was measured by 40 sensors buried in decomposed granite soil and crushed stone. For the diffusion behavior in the atmosphere, the concentration distribution was measured by Raman imaging. The hydrogen gas passing through the asphalt and diffusing into the atmosphere was irradiated with the third harmonic generation from the Nd: YAG laser, and the Raman scattering light was visualized by a high sensitivity camera. The characteristics of the hydrogen gas diffusion behavior were found. In addition, the hydrogen diffusion behavior was reproduced by simulation analysis, and compared with the experimental results. As a result, it is confirmed that the simulation of the diffusion behavior in the ground and in the atmosphere is valid even under the condition with pavement.