A gas chromatograph includes first and second sample vaporization units, first and second separation columns, first and second carrier gas suppliers, a column oven that contains the first and second separation columns and has a first heater, first and second detectors, a first auxiliary gas supplier that supplies an auxiliary gas to the first separation column and a controller that executes control by increasing a supply pressure of an auxiliary gas applied by the first auxiliary gas supplier to a pressure higher than a pressure during an analysis of a sample and lowering a supply pressure of a carrier gas applied by the first carrier gas supplier to a pressure lower than a pressure during the analysis of the sample such that the supply pressure of the auxiliary gas is higher than the supply pressure of the carrier gas, and sets a first maintenance switch mode in which the first sample vaporization unit is maintainable.