1. A post-processing agent application control device configured to control application of a post-processing agent to a recording medium by a post-processing agent application device, the post-processing agent application control device comprising: a first post-processing agent application amount determination unit configured to determine an amount of the post-processing agent to be applied to an image formed on the recording medium; a first glossiness determination unit configured to determine a first glossiness that is a glossiness of a non-image area of the recording medium in a case where the determined amount of the post-processing agent is applied to the non-image area; a comparison unit configured to compare a glossiness difference between the determined first glossiness and a second glossiness that is a glossiness of the non-image area of the recording medium, with a predetermined value; and a second post-processing agent application amount determination unit configured to, if the glossiness difference is larger than the predetermined value, change an amount of the post-processing agent to be applied, in a stepwise manner from an image area to the non-image area.