Objective : I would like to determine the main factors, in other words, the subjects that are responsible for febrile paroxysm and how they interact at the time of onset, based on the "Discourse on Hak(?)" chapter of "Huangdi Neijing(黃帝內經)". Methods : First, the pathological mechanism of the paroxysm was examined as described in the text. Then the subjects in question were analyzed based on the contents of the text. Result : 1. Febrile paroxysm happens when the three factors coincide at the Fengfu(風府). The three elements are as follows: first defense qi(衛氣), second latent qi(伏邪) and third, external pathogen(新邪). 2. Fengfu(風府) is not a specific point, but a region which external pathogen(新邪) passes through during which the defense qi is deficient. Conclusion : Febrile paroxysm is not caused by either an internal pathogen or an external pathogen, but the interaction between the three elements of the internal and external pathogens and the condition of defense qi. Moreover, the site, Fengfu(風府), which the disease is manifested is not a specific point but a more general region where the pathogenic qi has invaded while defense qi has weakened.