A gas chromatograph-mass spectrometer includes a gas chromatograph having a column that separates a sample into components, a mass spectrometer provided in a vacuum housing, and an interface that introduces a sample that has been separated into components in the gas chromatograph into the mass spectrometer, and the interface includes a partition wall fixed to the vacuum housing to close an opening formed in the vacuum housing, a line pipe that is fixed to the partition wall to penetrate the partition wall, includes a sample outlet line of the column and introduces the sample into the mass spectrometer, a heater that heats the line pipe in an axial direction, and a fixer that fixes the heater being in contact with the partition wall.