PURPOSE: To prevent even a fine amount of detection component from being left in a switching valve so as to gather a total amount by providing a virgin gas flow path in the upstream of the switching valve, so that a sample component, left in the flow path containing the inside of the switching valve, is extruded to a gathering side by virgin gas.

CONSTITUTION: A virgin gas flow path 26 is connected between itself and a three-way electromagnetic valve 14, which serves as a liquid chromatograph detector and a fraction collector, by a branch flow path connection part 28 in the upstream a little from the valve 14. The flow path 26 is constituted such that air is fed into a flow path 12 of the fraction collector via an air pump 22 and a two-way electromagnetic valve 24. A controller 30 performs control of switching to a gathering side outlet 15a and a discharge side outlet 15b of the valve 14 and control of opening/closing the valve 24. Timing of switching the valve 111 is based on a detection signal of the detector, and after a component, intended divided, is detected, the valve 14 is switched from the outlet 15b to the outlet 15a, at time of the first part of that component reaching the valve 14, and from the outlet 15a to the outlet 15b after extruding eluent by virgin gas.