To provide a putting-fold device, a paper post-processing device, an image forming device, and an image forming system that are not affected by air temperature, humidity, a temperature of paper, water content of the paper, and the like, and put a cease without image peeling.

The devices and system include: a paper temperature-and-humidity detecting means; an in-device temperature-and-humidity detecting means; a component temperature detecting means; a paper heating means; an in-device heating means; a component heating means which heats a component contacting with the paper; and a control means which refers to temperature-and-humidity information detected by the temperature-and-humidity detecting means and controls the paper heating means, the in-device heating means, and the component heating means to maintain the paper in the optimum temperature-and-humidity condition.