The present invention aims at reducing the time required for a series of analyses in the sequential performance of gradient analyses under a variety of conditions. To this end, in a control apparatus for controlling the operation of a liquid chromatograph having a gradient analysis function in which a mobile phase composed of a plurality of mixed solvents is used and a chromatograph analysis is performed while the mixture ratio of the solvents is temporally changed, the liquid chromatograph is controlled so as to continuously change the mixture ratio of the solvents from an initial mixture ratio to a final mixture ratio when performing a sample analysis; and as to perform, before the sample analysis, a preparatory liquid supply in which the mixture ratio of the solvents is continuously changed from the initial mixture ratio to the final mixture ratio at a rate higher than that in the sample analysis.