An image data coding apparatus having a coding unit that generates coded data after generating a transform coefficient by implementing Wavelet transform on image data, includes: a storage unit that stores coded data which the coding unit generates by coding image data which have not been sub-sampled; an information obtaining unit that obtains compression-related information indicating a compression rate or a restored image quality; and a re-coding unit that changes a sub-sampling ratio of individual color components constituting the coded data stored in the storage unit in conformance to the compression-related information and generates new coded data.