PURPOSE: To excellently and speedily perform pixel density conversion.

CONSTITUTION: This pixel density converting device is equipped with an interpolation part 1 which generates pixels corresponding to the deficiency in the resolution of an image of low resolution as unknown pixels and interpolates them when the image of low resolution is converted in pixel density into an image of high resolution to generate the image of high resolution, and an image process part 2 which sets values for the respective unknown pixels interpolated by the interpolation part 1. The image process part 2 determines the values of the respective interpolated pixels as known ones by using the values of pixels whose values are already known by regarding the respective unknown pixels of the image, into which the unknown pixels are interpolated, as completely unknown values and respective pixels in the area corresponding to the image of low resolution except the area of the unknown area as known pixels which all have known values.