A data processor transfers a data stream, which is stored on a storage medium, to a connected device. The data stream includes attribute information that specifies the format of the data stream. The data processor includes: an interface section, which communicates with the device to acquire format information about a format that is compatible with the device; a reading section for reading the attribute information and the data stream from the storage medium; a reading control section for determining, by the attribute information and the format information, whether or not the format of the data stream needs to be converted; and a converting section for outputting the data stream either after having converted the format of the data stream into the one specified by the format information or without converting the format of the data stream as determined by the reading control section. The interface section transmits the data stream, which has been output from the converting section, to the device.