1. An image data processing device that generates driving image data used to drive an image display device with an LCD, the image data processing device comprising: an image memory that sequentially stores input image data of multiple frames; a write control module that controls a writing operation into the image memory; a read control module that controls a reading operation from the image memory; and a driving image data generation module that generates the driving image data from read image data sequentially read from the image memory by replacing at least part of the read image data with regard to selected pixels with mask data, the driving image data being data for driving the LCD of the image display devices, the driving image data generation module generates first driving image data and second driving image data by arranging the read image data and the mask data alternately on every ‘m’ horizontal lines in an image displayed by the image display device, where ‘m’ is an integer of not less than 1, and the first driving image data and the second driving image data having different sequences of the read image data and the mask data, wherein: the mask data is set corresponding to a pixel value of the read image data in each of the selected pixels to be replaced with the mask data, the mask data is generated by a preset operation of the read image data with regard to the selected pixels to be replaced with the mask data, based on a specific parameter set according to an amount of motion of a whole image expressed by the read image data, and the specific parameter is set to vary a ratio of the mask data to the pixel value of the corresponding read image data in a value range of 0 to 1 and to give a smaller ratio against a greater amount of motion and a greater ratio against a smaller amount of motion.