A chromatography system has a multi-channel detection device including a flow cell, optics for directing light from light sources to the flow cell and outputting light that has passed through the flow cell, and a multi-channel detector. The optics has a function of dispersing light in wavelength in an optical path. The detector receives the light dispersed in wavelength. The multi-channel detection device also has a signal processing part connected to the detector. The chromatography system has a data processing apparatus. The signal processing circuit has a function of calculating an absorbance by absorbance=−log10(I/I0) using the intensity I of light having a wavelength to be measured that is outputted from the detector and a reference intensity I0 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.