A sample is introduced from an injector unit into a mobile phase. One target component is separated into a plurality of vials by a fraction collector. Next, a sampler sequentially suctions the eluate from the plurality of the vials and performs an LC analysis on each of the eluate portions, thereby producing a chromatogram. A peak detector calculates the peak area corresponding to the amount of the target component in each chromatogram. A delay estimator extracts the peak area in the fraction having the maximum peak area and the peak areas in the previous and succeeding fractions on the time axis of the foregoing fraction. Then, the delay estimator estimates a delay volume from a detector to the tip end of the dispenser nozzle based on data such as the peak areas, the flow rate of the liquid fed from the pump, positions of the vials, and the position of the peak of the target component in the chromatogram detected by the detector, and stores the delay volume. Upon preparative separation of a desired component, a delay time is calculated based on the delay volume and the flow rate and the timing for the preparative separation is controlled based on the delay time.