A reference sample having a known concentration is injected into a chromatograph system before an unknown sample is analyzed. This is for the purpose of checking the deterioration of system performance or in other words for the purpose of checking system suitability. In the present invention, the chromatographic characteristic of the check sample at the time of deterioration of the system suitability is expected and stored in a memory in advance to be related to factors of deterioration of system suitability. A factor of deterioration is deduced by comparison between the actually analyzed chromatographic characteristic of the check sample and the relational data stored in the memory. A guidance required for removing the factor is displayed. Disclosed are preferred embodiments of a chromatograph system suitable for analyzing catecholamine or glycated hemoglobin.