A gas analyzing system that can perform calibration without being influenced by the deterioration of span gas in a span gas supply line. An open-close device control part that receives a calibration start signal issuing an instruction to start zero calibration and span calibration, and controls an open-close device for a span gas flow path. An open-close device for a zero gas flow path, wherein if the open-close device control part receives a new calibration start signal after a predetermined time has passed since previous calibration was performed, before the span calibration is started, for a predetermined time, the open-close device control part controls the open-close device for the span gas flow path so as to open the open-close device for the span gas flow path, and thereby purges span gas that remains in the span gas flow path.