To obtain a printer which makes data management more effectively and a data managing method for the printer.

The printer 1 has functions of receiving and stoning print data from a PC client 2 of a host into a storage device 11 and then printing the data with an indication from the user. The printer has a resolution decreasing process part for lowering the resolution of the print data in the storage device 11 by using a CPU 12, a ROM 13, and a RAM 14. When there is no print indication from the user for a predetermined time, the resolution decreasing process part lowers the resolution of the print data in the storage device 11 to expand the unused area in the storage device 11. Consequently, the amount of information is reduced by lowering the resolution of image data left in the storage device without being printed to release resources (storage area) to other users, and the shared printer can be used with efficiency.