To provide an image quality adjustment system in which the image quality adjustment corresponding to mechanical characteristics and the image quality adjustment corresponding to the user's preference and the using environment can be easily and quickly executed, and at the same time, the management of the mechanical characteristics and the adjustment software of an image forming device can be easily executed in the image forming device.

The image forming device 1 transmits the user instruction information and the characteristic information of a printer and a scanner to an external controller 2 in the image quality adjustment system 100. The external controller 2 calculates the adjustment parameter on the basis of the user instruction information and the characteristic information which are transmitted from the image forming device 1. It transmits the calculated adjustment parameter to the image forming device 1. Image processing is applied to the image data on the basis of the adjustment parameter transmitted from the external controller 2, and the processed image data are outputted from the printer part in the image forming device 1.