PURPOSE: To enable a reference peak to be identified more accurately by determining the reference peak based on a difference in reference to a preset standard holding time for a peak-holding time and a standard sample.

CONSTITUTION: When a means for detecting the number of peaks detects two or more peaks within an identification allowable width T, a calculation means calculates a holding time ti of each peak, each peak area or a height, and an area ratio Ai/Ao between a maximum peak area Ao and another peak area or a height ratio. Then, a criterion means identifies the maximum peak as a reference peak when no peaks exceeding a specified ratio exist. On the other hand, when no peaks exceeding a specified ratio exist, the criterion means obtains a difference between its peak time (ti) and a standard holding time (to) for a reference sample and that between a maximum peak holding time and the time (to). Then, by comparing these two differences, a peak which is closest to the time (to) which is preset for the standard time is identified as the reference peak.