Disclosed are a threshold value data setting device, method, and program and an image forming system capable of, even if the number of types of printing devices and printing materials is enormous, simply and easily determining threshold value data suitable for any combination thereof. A change in dot shape occurring in an image forming process from the creation of a binary image signal 46 to the formation of an image is acquired as response characteristics data 112 in a spatial frequency domain. The response characteristics data 112 is applied to create a simulated image signal in which the change in dot shape is reproduced in a simulated manner. Threshold value data 44 to be set is determined from among threshold value candidates by a comparison and/or evaluation based on quantitative values calculated by executing predetermined evaluation processing for the simulated image signal.