The present invention aims to provide a liquid chromatograph, an analysis system, and a gradient elution method, which are designed to permit a gradient change of eluent with higher precision and also permit a high sensitive detection or analysis. For attaining the object, there are provided: a liquid chromatograph having at least a liquid-feeding means for flowing an eluent E at a predetermined flow rate, a sample-pouring means for pouring a sample Sm into the eluent E, and a separation-column means for separating a solute So contained in the sample Sm into components, comprising an eluent-selecting means for forming branched flow paths having predetermined volumes by dividing a flow path of the eluent E fed from the liquid-feeding means, temporally storing eluents E.sub.1, E.sub.2, and soon in the branched flow paths, and pouring the sample Sm into the selected eluents E.sub.1, E.sub.2, and so on, and means for carrying out a gradient elution of a solute So; an analysis system comprising a mass spectrometer connected to the liquid chromatograph, and a gradient-elution method using the liquid chromatograph.