A detector for liquid chromatograph includes a light source, a flow cell that includes a linear capillary, a holding member that holds one end portion of the capillary, an entrance port for allowing light to enter one end of the capillary, and an emission port for allowing light to be emitted from another end of the capillary, a condensing mirror for guiding light from the light source to the entrance port, and a light receiver for detecting the light emitted from the emission port, a lens is provided between the one end of the capillary and the condensing mirror, and the lens is arranged so as to parallelize light in a center region around an optical axis among light directed to the one end of the capillary from the condensing mirror and distance a first reflection position of the light in the center region from the one end.