An image data processing apparatus includes the following elements. A lossless compression device performs lossless compression. A configuration controller performs control so that a first configuration including a first line memory set and a decompression circuit set and a second configuration including a second line memory set are selectively set in a reconfigurable circuit. A maximum size determining device determines the maximum size of lines of the compressed image data. An output controller performs control so that, when the maximum size is equal to or smaller than a predetermined threshold, the first configuration is set and the compressed image data is output to an image processing circuit via the first line memory set, and so that, when the maximum size is greater than the predetermined threshold, the second configuration is set and the non-compressed image data is output to the image processing circuit via the second line memory set.