To enable suitably heat the inside of an agricultural greenhouse or the like while performing fermentation processing of organic waste using fermentation tank and utilizing the fermentation heat.

A fermentation heat utilizing system includes the fermentation tank 1 for fermentation processing the organic waste, a high-pressure blower 10 for blowing compressed/heated air from a bottom part of the fermentation tank 1 toward the organic waste in the fermentation tank 1, and a jacket 11 covering an outer surface part of the fermentation tank 1. Heating fluid for absorbing the fermentation heat generated by the fermentation of the organic waste in the fermentation tank 1 flows inside the jacket 11. The heating fluid circulates between the jacket and a radiation part 20 arranged in a specific heating zone.