The content processing device includes a first converter for performing first conversion processing of converting frame rates of the first content and the second content, which are moving images, so that the frame rates become equal to each other, a synthesizer for performing screen synthesis for displaying side by side the conversion results on the same screen, a second converter for performing a second conversion processing of converting the frame rate of the synthesis result to a frame rate higher than the frame rate before being converted, a storage unit for temporarily storing the frames required for the first conversion processing and the second conversion processing, and a controller for calculating a ratio of storage capacities of the storage unit to be assigned to the first conversion processing and the second conversion processing according to attributes related to motion amounts of moving images.