To effectively carry out the gray-scale conversion of a medical image according to the gray-scale of a medical image output device to secure the compliance of the medical image.

In the image gray-scale conversion responding to the gray-scale characteristic of the image output device, a control section 11 determines the gray-scale characteristic of the medical image according to accompanying information of the medical image input from an image generation device, carries out image processing so as to respond to the gray-scale of the image output device of the output side by referring to an image output device information file 172, and thereafter performs output to the image output device of an output side.