In distributing moving image data, it is an object to make it possible to start reproduction, not only from the head of the moving image data, but also from any desired position and to minimize an increase in the amount of the processing. A moving image data conversion device (1) comprises moving image data receiving means (2) for receiving moving image data (6), decoder configuration information saving means (3) for retrieving and holding decoder configuration information included in the moving image data (6) to define a condition for decoding the moving image data (6), decoder configuration information inserting means (4) for inserting the decoder configuration information into a plurality of predetermined positions in the moving image data (6) to generate moving image data, and moving image data output means (5) for outputting the generated moving image data as moving image data (8).