PURPOSE: To facilitate the maintenance of an apparatus, by performing a temperature control of a valve unit for altering passages, a molecule composition fractionation unit and a molecule size fractionation unit with respective independent automatic temperature controllers.

CONSTITUTION: Heating containers of a passage altering valve unit A having an internal reference liquid injection mechanism which includes a sample polymer solution injection port, a sample polymer solution determination loop, a liquid determination loop and a liquid injection valve and a valve for altering system passages, a molecule composition fractionation unit B and a molecule size discrimination unit C are connected to automatic temperature controllers Aa, Ba and Ca respectively and set for a temperature enough to guarantee a free passage of a polymer solution independently. The control of the automatic temperature controllers Aa, Ba and Ca and valves within the unit A is performed with a system controller Ab. This accomplishes an independent temperature control for the units A, B and C thereby facilitating the maintenance of the apparatus.