PURPOSE: To effectively store printing output data whose classifications are different in the prescribed capacity by changing arbitrarily the storage capacity corresponding to each printing data set to a storage medium based on a control code.

CONSTITUTION: Based on a control code instructed from an external equipment 2 to be an external host, a storage capacity allocation corresponding to each printing output data set to a RAM 16 being a storage medium is designated. Consequently, a changing means 13a changes arbitrarily the storage capacity allocation corresponding to the data set to the RAM 16, and the printing output data whose classifications are different are stored effectively in the RAM 16 of the prescribed capacity. In this case, the using rate of each allocation storage area of the RAM 16 is informed to the external equipment 2 by an informing means 13b, and the changing means 13a executes an optimal memory allocation. In such a manner, to the RAM 16, an optimal memory environment is set, and the data is stored effectively as to its classification.