In the Northern Song[宋] Dynasty, the iron coin was changed with several reasons. For solving the lack of the amount of the coins in circulation in Sicuan[四川] province and the financial crunch of the central government, the government minted iron coin that costs less expensive and issued the official Jiaozi[交子] to cut down on coinage charges. However, the financial crisis became worse because of the war with Western Xia[西夏] during the era of Xining[熙寧, 1068-1077]. In Shaanxi[陝西] province, the iron coin was minted in large quantities and flowed down into Sicuan province. The inflow of iron coin led to the devaluation of iron coin in Sicuan province. In the Northern Song, the iron coin of Sicuan province underwent the three huge changes. First, the government implemented a policy in Sicuan province after the occupation of Shu[蜀]. It caused the rapid decrease in circulation of cooper coin. In Sicuan province, both cooper coin and iron coin had been circulated. However, iron coin was only used in Sicuan province after the implementation of the policy. Second, the large iron coin of Jinde[景德大鐵錢] and Xiangfu[祥符大鐵錢] were minted during the regime of Emperor Zhenzong[眞宗]. The government minted the coin of Jinde and circulated to solve the lack of the amount of the coins in circulation. However, the government ignored the drawback of the coin that it is differ between the nominal value and real value. The drawback caused 'the lack of the amount of coins in circulation and resulting inflation[錢輕物 重]. The solution to resolve the drawback of the coin was casting small iron coin or cooper coin in bulk and circulating them in Sicuan province. However, the government newly minted the coin of Xiangfu that the weight is half of the old coin and put that into circulation because of the shortage of coins and the government's financial crunch. Third, in the regime of Zhenzong, a phenomenon that the supply of iron coin was outstripping demand occurred after issuing unofficial Jiaozi and the coin of Xiangfu during the era of Jiayou[嘉祐, 1056-1063]. Therefore, the casting iron coin was discontinued for a decade from 1059 year[嘉祐 4]. After the issuing unofficial Jiaozi, most of the iron coin in Sicuan province stored as the reserve fund of Jiaozi with the government issued Jiaozi. As increasing the amount of Jiaozi that was issued, the demand of iron coin was decreased. The policy that stopping the casting for 10 years, the price had stabilized. However, because of the overissue of Jiaozi, the policy had been of no effect. Jiaozi was appeared instead of iron coin that is inconvenience to use. That story has been cast in stone as historical fact. The appearance of Jiaozi was possible due to Sicuan province economically developed with the weight of iron coin. However, the excessive issuance of Jiaozi caused it's depreciation of the currency. After all, Jiaozi was replaced a new form of bank note called Qianyin[錢引]. In the era of the Northern Song dynasty, Sicuan province was a particular area in the people's economic activity. The rest of the Song dynasty was able to use both cooper and iron coin. However, iron coin was only used in Sicuan province. This caused the boost in prices, 'the lack of the amount of coins in circulation and resulting inflation', and the falling iron coin. One of the biggest causes of the falling iron coin was the financial deficit of the Song government. In the end, Sicuan province was the particular monetary economy area to resolve the lack of finance of the Song dynasty.