A gas leak detection device includes a learning section, which has a correlation between a gas temperature inside gas pressure containers and a surface temperature of the gas pressure containers in a learning period corresponding to a current value flowing in the conductor, to make database, and a diagnosis section, which extracts a gas temperature corresponding to the measured current value and the surface temperature from the learning section in a diagnosis period, corrects a gas pressure value corresponding to an arbitrary surface temperature to a gas pressure value of a reference temperature using the extracted gas temperature, and detects a leak of the insulating gas based on the corrected gas pressure value.