Abstract: In a printing apparatus such as a laser beam printer, the time required for decomposing format data into dots is compared with the printout time for a page. If the former is not longer than the latter, both format data and description (e.g. character) data are decomposed into dots in the same one of a couple of memories and said couple of memories are alternately and cylically brought to store operation and printout operation. If, on the contrary, the former is longer than the latter, the decomposed format is fixed in one memory while description data is decomposed every time in the other memory, and the contents of both memories are superimposed when printed out.