To realize prior printing of a classified document by interrupting the printing of other documents.

When the user inputs the identification number of a classified document to an identification number inputting portion 105, a memory information managing portion 104 retrieves an identification information memory portion 103 so that in the case the identification number is found, printing of the classified document information corresponding to the identification number is required to a printing controlling portion 106. The printing controlling portion immediately starts printing in the case a printing portion 108 is not printing, or interrupt printing in the case the printing portion 108 is printing and sends page feed information as well as the printing interruption position is stored in a printing information memory portion 107 for prior printing of the classified document. However, in the case the printed document is also a classified document, the above-mentioned operation is not conducted. Further, printing of the interrupted document will be resumed after finishing the classified document printing.