1. An image processing apparatus used for displaying an image obtained from an inputted image signal on an image display, the image processing apparatus comprising: an attribute information determining unit which obtains first attribute information indicating the format of the inputted image signal and second attribute information indicating transmission characteristics of the image signal; an image quality adjustment value calculating unit which calculates image quality adjustment values for the image signal based on the first and second attribute information obtained by the attribute information determining unit; and an image processing unit which adjusts the image quality of the image signal based on the image quality adjustment values calculated by the image quality adjustment value calculating unit and then outputs the image to the image display, wherein the image quality adjustment value calculating unit, calculates an image quality evaluation value (P) by the formula (P=Br/Re/Fr) of the bit rate (Br), Resolution (Re) and frame rate (Fr) included in the second attribute information. fixes an image quality evaluation reference value (P0) based on a value calculated by applying the reference bit rate, reference resolution and reference frame rate defined for each format in the first attribute information to the above formula, calculates an image quality evaluation value ratio (Pr) by the formula (Pr=P1/P0) of an image quality evaluation value (P1) of the video image file to be displayed and the image quality evaluation reference value (P0) corresponding to the format, and decides the image quality adjustment value for the image signal using the image quality evaluation value ratio (Pr).