The invention relates to an apparatus for preparing pure carbon dioxide (CO.sub.2) from a gaseous CO.sub.2 containing product, which apparatus comprises a processing line which comprises at least an inlet for the gaseous product, means for removing water-soluble impurities from the product, compression means for compressing and pressurising the product, cleaning means for removing further impurities from the product, as well as storage means for collecting and storing the purified CO.sub.2, which elements are interconnected by means of suitable piping. According to the invention, the compression means comprise at least one screw compressor so as to provide an apparatus for preparing pure carbon dioxide from a gaseous CO.sub.2 containing product which has a higher efficiency, which is of simpler, cheaper construction and which is easy to maintain.