A controller for controlling the operations of an autosampler, a sample push unit, and a make-up unit includes a pump stop timing setting unit for setting a first timing T1 of completion of dilution of a sample, and a subsequent second timing T2 of completion of trapping of a sample in the trap column, a dilution control unit for causing a solvent delivery pump for make-up of the make-up unit to operate, and for stopping operation of the solvent delivery pump for make-up at the first timing T1 set by the pump stop timing setting unit, and a sample push control unit for causing a solvent delivery pump for sample push of the sample push unit to operate, and for stopping operation of the solvent delivery pump for sample push at the second timing T2 set by the pump stop timing setting unit.