An information input/output system capable of reliably preventing improper leakage of information and of keeping confidential information secret. The information input/output system provides a digital copying machine compositely having a plurality of functions, such as a filing function, an OCR function, a facsimile function and a network function. The digital copying machine performs an information retrieval on the basis of a password from a user in response to an information retrieval requirement (information retrieval request) made through its operating section, an information retrieval requirement made by a information retrieval sheet sent from the external through the use of a facsimile or an information retrieval requirement made through a personal computer on a network. After the completion of the information retrieval, the digital copying machine issues a new password (for example, at random) and makes the previously used password invalid.