A chromatography system has a multi-channel detection device 10 including a flow cell 12 to which a specimen is supplied, optics for directing light from light sources 11 to the flow cell 12 and outputting light that has passed through the flow cell, and a multi-channel detector 13 disposed on an output of the optics. The optics has a function of dispersing light in wavelength in an optical path. The detector 13 receives the light dispersed in wavelength. The multi-channel detection device 10 also has a signal processing part 14 connected to the detector. The chromatography system has a data processing apparatus 20. The signal processing circuit has a function of calculating an absorbance by absorbance = -log 10 ( I / I 0 ) using the intensity I of light having a wavelength to be measured that is outputted from the detector and a reference intensity I 0 of light that is an average of intensities of light having different wavelengths that is produced at the same point of time as the light having a wavelength to be measured.