To provide a stencil printing apparatus capable of preventing leakage of secret due to an afterimage phenomenon even when a secret document is subjected to plate-making and printing and left for a long period of time.

The stencil printing system 1 includes a random plate-making and winding mode specifying means 2 for specifying effectiveness/ineffectiveness as to whether or not a master is newly subjected to plate-making by an irregular plate-making pattern and loaded on a printing drum after the completion of printing, when the document is subjected to plate-making and printing; an image size/position storage means 8 storing the image size and position on the master of the document finally subjected to the plate-making and printing; a time counting means 3 measuring the lapse of time from a time point when the plate-making and printing of the document is finally performed; and a winding master information storage means 9 storing the state whether the master wound around the current printing drum is subject to random plate-making winding.