In order to clarify the effects of gravity on deflagration phenomena, we conducted flammable gas explosion experiments using a constant volume combustion vessel under several gravity level from earth gravity (1 G) to elevated gravity up to 50 G. The elevated gravity field was formed by a centrifuge. We observed the expanding flames in hydrogen-air, methane-air, and propane-air mixtures by a high-speed camera and measured explosion pressures in the vessel. Lean and rich flammablility limits were determined by the records of the explosion pressures, and it was confirmed that the flammable range were approximately same regardless of the gravity level. In the methane-air and propane-air conditions, the shapes of the propagating flames changed dramatically with increase of gravity due to strong buoyancy effect, especially in lean and rich flame conditions with slow burning velocity. Also, with increase of gravity, maximum overpressure and maximum rate of pressuer rise decreased except the case of hydrogen-air flame with higher burning velocity.