A liquid chromatograph mass spectrometer specifying a location where a flow path is clogged and recovering in a short time. The liquid chromatograph mass spectrometer includes a first flow path passing through a separation column, a second flow path not passing through the separation column, a mass spectrometry unit on the downstream side of the first and second flow paths that analyzes a sample that has passed through the first flow path, a first valve for connecting any one of the first and second flow paths to the mass spectrometry unit, and a controller for controlling driving of the first valve connecting the first flow path to the mass spectrometric unit, comparing the measured value of the mass spectrometric unit with a predetermined threshold value, and connecting the second flow path to the mass spectrometry unit when it is determined to be abnormal.