Kokaho (price regulation law) is a law that stipulated the official prices and the conversion rates for goods at the market from ancient times to medieval periods under the Court, kokuga (provincial government offices) and the Kamakura bakufu (Japanese feudal government headed by a shogun). The prices based on the law were called koka, which were used as standards for calculating taxes paid in kind, prices in trading and conversion rates for goods.
Taiho Code defined the koka in the cities on both east and west of the capital, and the koka for in-kind payment of taxes on trade or taxes on fields administered directly by a ruler (jishi), such as kubunden (the farm land given to each farm in the Ritsuryo system) (or when conducting jishi trade in order to send jishi (land taxes under the Ritsuryo system to the central govenment)).
But the Daijokanpu issued in 798 (official docments issued by Daijokan, Grand Council of State) ordered ryoseikoku (province) to buy at Washi price (present-day market price) when purchasing local specialties (trading miscellaneous things) to deliver to the Court. The reason for this was not only that there were differences between koka and washi prices but also that there was no end to the corrupt practices by kokushi (provincial governors) at kokuga and Zaichokanjin (the local officers in Heian and Kamakura periods), who imposed unreasonably low prices as koka on local residents, buying more goods than necessary so that they could use the surplus to feather their nests. However, with the elimination of Kocho-Junisen (twelve coins casted in Japan), circulation of currency fell, and on the other hand, with the wide-spread use of in-kind tax payments and purchasing goods from the trade related to the in-kind tax payments to deliver to the central government, koka was called for as the standards for prices. In addition, koka was required to stabilize the prices in the capital (Heian-kyo) and to control foreign trade in Dazai-fu (local government offices in Kyushu region) (because the imported goods were mostly consumed in Heian-kyo, prices there and foreign trade were closely related).
As a result, Kokaho continued after that, and in 914 the law permitted changing the koka in local kokuga that had been uniform throughout the country (1 roll of silk = 50 bunches of rice plant, 1 roll of cotton = 5 bunches of rice plant), and in 947 it ordered Kinai region (provinces surrounding Kyoto and Nara) and Tanba Province to reduce koka to suit the actual conditions. Later on, prices were regulated in 962, 986, 1072, and 1179 under Kokaho. It is considered that the regulation in 1179 among others was one of the causes of the Coup of the Third Year of Jisho staged by TAIRA no Kiyomori because banning the use of Sung money, the main source of the Taira clan government's revenue, was proposed by Cloistered Emperor Goshirakawa's wishes in the same year. Afterwards, Kokaho was issued in 1195, 1249, 1250, 1253, 1282, and 1330. Acting in concert with the Kakoho of 1253, the Kamakura bakufu set official prices in that year and the following year.