To provide an energy supply device for use in an aircraft, which generates toxic material and noise less than that in a prior art and has an improved efficiency.

In this energy supply device inside an aircraft which is converted for a main driving device, an auxiliary driving device, a ram air turbine, or a NiCd battery, waste gas from an air conditioner of the aircraft or external air out of the aircraft is used for air supply to a fuel cell 1 generating direct current, water is provided from the waste gas from the fuel cell 1 for water supply to the aircraft, at this time, the waste gas from the fuel cell 1 is subsequently introduced to the periphery 5 of the aircraft, and hydrogen from the fuel cell 1 is introduced to the periphery 5.