Recently, 5-amino-1H-tetrazole is developed for practical use as a substitute for sodium azide, which is conventionally used as a fuel component of gas generating agents for automobile airbags. In this study the combustion mechanisms of the mixtures 5-amino-1H-tetrazole/potassium nitrate and 5-amino-1H-tetrazole/sodium nitrate have been examined. It has been found that the Granular Diffusion Flame model is applicable to the tested samples even when a molten layer exists at the burning surface. In addition, it is shown that within the pressure range of 1 - 5 MPa, the greatest factor which affects the burning rate is the diffusion process. It is also demonstrated that the fuel component decomposes first, and the oxidizer decomposes next. Meanwhile, it has also been confirmed that the burning rate increases with an increase in pressure because the flame approaches the burning surface and the amount of heat transfer to the solid phase increases. In spite of a decrease in the amount of heat transfer from the gas phase to the solid phase and an increase in the thickness of the condensed phase reaction zone for a mixture with higher fuel content. there are little differences in the burning rates probably because of an increase in the rate of decomposition of the solid phase.