Jomai originally means the annual rice tax from Edo bakufu directly controlled land (so-called 'tenryo'), but later, it means the rice stocked by the bakufu or fudai daimyo domain (a domain of a daimyo in hereditary vassal to the Tokugawa family) as provisions of rice for the army. It is also called oshiromai or shirotsukemai. By 1730, it was renamed as goyomai to distinguish it from jomai which means the annual rice tax of dominion under direct control of the bakufu.
A prototype existed in the Toyotomi government era, where a position of jomai bugyo (a magistrate of administering the annual rice tax) was created and Masanori FUKUSHIMA and Takamasa MOURI were appointed. The Edo bakufu succeeded this policy, stockpiling rice surpluses from the directly controlled land as provisions of rice for the army in case of emergency, and further expansion of the system was needed when Kanei era started, so fudai shohan (domains of hereditary vassals) were provided with the annual rice tax or goyokin (the money the Edo bakufu charged temporarily on farmers and merchants) and ordered to stockpile and administer the rice in 1633. Three years later, an exclusive institution was established in Asakusa okura in Edo, and jomai bugyo was appointed. The bakufu ordered jomai bugyo and fudai shohan to change the jomai every year and prepare for emergency, and when fudai domains changed the territory, they were required to check whether there is jomai stock based on regulations and the policy of the stock. After that, in 1661 and 1685, the bakufu ordered to increase the jomai stock, and it also adopted the same measure to shukuba-machi (post station) in Tokaido.
According to the system of 1685, 442,000 koku (approximately 79.6 million liters of crop yield) of jomai was stocked all over Japan, and it was dispersively stocked in totally 68 places such as castles in the bakufu directly-controlled lands or in fudai domains (the Edo-jo Castle, Osaka-jo Castle, Nijo-jo Castle, Sunpu-jo Castle) or shukueki (post town), and also, in 1673, the bakufu hired private cargo-vessels and used them as dedicated vessels (jomai sekisen) to carry jomai to specified places where jomai was stocked. Jomai sekisen were paid a large amount of money, but instead, they were strictly controlled by the bakufu and they were prohibited from carrying goods other than jomai. Bakufu's requirement was so strict that the number of jomai sekisen decreased, and then in 1743, the bakufu allowed jomai sekisen to carry general cargo under its license system.
At that time, because of the long-lasting peace, jomai which was originally stockpiled for the purpose of the military was gradually being used as a redress for the disaster such as famine, or diverted to the resources of extraordinary expenses, and finally, in 1689, the bakufu put the criteria of stock back before Kanbun era to cover the deficit of its financial affairs and sold the surplus rice. It is believed that the background that led to the change of jomai to 'goyomai' in 1730 was closely related to the actual situation of the time where the stock was used for disaster relief or financial adjustment and military significance was faded. Later on, goyomai was used to relieve the Great Famine of Kyoho or the Tenmei Famine, but in Kansei reform by Sadanobu MATSUDAIRA, kakoimai (it refers to the system where rice was stored by the bakufu, clans and towns and villages in case of emergency) was introduced as a substitute for goyomai and the bakufu tried to revive original goyomai used for military purpose only. However, it was still being used as a purpose of disaster relief or finance because the situation of the bakufu's finance was getting worse.