Abstract: A data processor having a page turning function, for managing a plurality of data sets each containing a plurality of data units of different kinds, has an extraction portion, a decision portion, and an output control portion. The extraction portion is used to extract a data unit in a page ahead of the present page in response to a next page instruction, or in a page behind the present page in response to a previous page instruction, and the decision portion is used to determine whether or not the kind of the data unit extracted by the extraction portion is equal to the kind of a data unit in the present page. The output control portion is used to provide the data unit extracted by the extraction portion if the decision portion determines that they are equal to each other, and if the decision portion determines that they are unequal to each other, restarting the extraction process of the extracting portion. Therefore, the page turning operation can be rapidly and easily carried out.