A controller 103, based on the positional information of the display image, selects whether the 3-dimensional image data decoded by a decoder 102 is displayed stereoscopically (in 3-dimensional display mode) or planarly (in 2-dimensional display mode) and gives notice of the selected display mode to a display portion 104. Specifically, the input positional information=display address is monitored, and if no temporal change occurs, namely if the displayed position of the image data does not change, 3-dimensional display mode is selected as the display mode. On the other hand, if there is a temporal change, namely if the displayed position of the image data varies by scrolling, 2-dimensional display mode is selected as the display mode. Thus, an image data display apparatus which can efficiently display image data on a display when display of 3-dimensional image data is scrolled is provided.