Information associated with data which was previously transmitted to a client terminal (201 or 202) is recorded as a history. When a transmission request of data of logical units in tiles required to obtain a desired image is received from the client terminal (201), the type of progression order used in the client terminal (201) is discriminated with reference to the history. The transmission order of the data of the logical units in the tiles to be transmitted to the client terminal (201) is determined in accordance with the discrimination order, and the data of the logical units in the tiles are transmitted to the client terminal (201) in accordance with the determined transmission order.