A two-dimensional liquid chromatograph includes a first-dimension separation channel for guiding a sample injected from a sample injection part to a first-dimension analysis column using a first-dimension analysis mobile phase for separation; two trap columns; an analysis channel for guiding components retained in the trap columns to a second-dimension analysis column using a second-dimension analysis mobile phase for analysis; and a channel switching mechanism. The switching mechanism connects the first-dimension separation channel to one of the trap columns and connecting the analysis channel to the other of the trap columns, and also switches connections between the trap columns and the channels.