A liquid chromatograph control apparatus (1) includes a measured value storage (25a) that stores a measured retardation factor (Rf) value of a sample (3), which is obtained when components of the sample are separated on thin layer chromatography using eluent (4) containing a plurality of ingredients at a specified mixture ratio, in association with the specified mixture ratio, a rate-of-change-in-Rf-value storage (25b) that stores a rate of change in the Rf value of the sample (3) with respect to variation in mixture ratio of ingredients of eluent (10), a mixture ratio calculator (22a) that determines a mixture ratio of the eluent (10) at which a specified retardation factor value (RfO) of the sample is obtained, based on the measured Rf value corresponding to the specified mixture ratio stored in the measured value storage (25a) and on the rate of change in the Rf value stored in the rate-of-change-in-Rf-value storage (25b), and a mixture ratio controller (22b) that outputs a control signal to control the mixture ratio of the eluent (4) fed into a column (18) so that the Rf value of the sample (3) can be equivalent to the specified retardation factor value (RfO), based on calculated results by the mixture ratio calculator (22a).