The invention provides an image adjusting apparatus for receiving a set of input signals transmitted from a video interface, which is used for receiving a plurality of sets of input signals. The image adjusting apparatus is further used for automatically adjusting the set of input signals to generate a set of output signals. The image adjusting apparatus includes an operation module, a storage module, an offset module and a gain module. The operation module receives a test image to generate a plurality of adjusting signals. The storage module stores the adjusting signals. The offset module transforms, according to the adjusting signals, the set of input signals into a set of temporary signals. Moreover, the gain module transforms, according to the plurality of adjusting signals, the set of temporary signals into the set of output signals.