An apparatus and a method for converting multi-source input images are disclosed. The apparatus includes an outside interface part including N outside interface units and pre-processing the input image, a format converting part including N format converters and converting formats and sizes of the pre-processed images as required by a display device, a memory part interacting with each format converter and storing each pre-processed image or format-converted image, a switching part switching the format-converted images according to a display mode, a multiplexer multiplexing the switched images and generating a corresponding display image, and a display processor processing the display image for the display device. Therefore, various input images can be properly converted to have desired formats and sizes based on a display mode of a display device so that the converted multi-images can be adequately displayed on a display device.