To reduce an arithmetic processing load or an influence of noise at the time of virtual curve calculation processing, provided is a data processing device for a chromatograph, which is configured to execute data processing based on plot data measured by using a chromatograph, the data processing device including a virtual curve calculation data generator configured to obtain a smaller number of pieces of virtual curve calculation data than a number of pieces of the measured plot data; and an arithmetic processor (163) functioning as a virtual curve calculator configured to obtain a virtual curve based on the virtual curve calculation data.