When data to be output in accordance with a predetermined protocol and attached information of the data are input in setting output conditions of an output apparatus capable of setting a plurality of output parameters, information concerning output of the data is detected from the attached information. An output parameter is selected in accordance with the detected information, and the data is converted in accordance with the selected output parameter. This reduces operations by a user, so an appropriate output corresponding to the data can be obtained without any expert knowledge. This invention is applicable to, e.g., an output system for printing medical images.