In an image data processing apparatus, a conversion unit generates first image data of a first image format and second image data of a second image format and supplies the first and second image data on a time division basis with respect to each image taken by using an image sensor. An operating unit acquires the first and second image data produced on a time division basis from the conversion unit, performs a process for displaying the taken image on a display device by using the first image data, and performs a process for storing the taken image in a storage device by using the second image data.