Provided is a jet system capable of regulating a pressure of a jet substance without using any high-pressure gas supply subsystem. In a storage section for storing therein a jet substance such as fuel or oxidizer, a pressurizing substance such as liquefied gas is stored in addition to the jet substance, to enable the jet substance to be supplied from the storage section according to pressurization from the pressurizing substance. A jet operation is performed while an internal pressure of the storage section lowered along with discharge of the jet substance therefrom is at least partially recovered by at least a part of the pressurizing substance vaporized in the storage section.