第29章為替相場と国際資金移動

Most countries have different currencies, but not all. Sometimes small economies use an economically larger neighbor's currency. For example, Ecuador, El Salvador, and Panama have decided to dollarize—that is, to use the U.S. dollar as their currency. Sometimes nations share a common currency. A large-scale example of a common currency is the decision by 17 European nations—including some very large economies such as France, Germany, and Italy—to replace their former currencies with the euro at the start of 1999. With these exceptions, most of the international economy takes place in a situation of multiple national currencies in which both people and firms need to convert from one currency to another when selling, buying, hiring, borrowing, traveling, or investing across national borders. We call the market in which people or firms use one currency to purchase another currency the foreign exchange market.

You have encountered the basic concept of exchange rates in earlier chapters. In The International Trade and Capital Flows, for example, we discussed how economists use exchange rates to compare GDP statistics from countries where they measure GDP in different currencies. These earlier examples, however, took the actual exchange rate as given, as if it were a fact of nature. In reality, the exchange rate is a price—the price of one currency expressed in terms of units of another currency. The key framework for analyzing prices, whether in this course, any other economics course, in public policy, or business examples, is the operation of supply and demand in markets.

If you travel to a foreign country that uses a different currency, you will undoubtedly need to make a trip to a bank or foreign currency office to exchange whatever currency you’re holding for that country’s currency. Even though this is a simple transaction, it is part of a very large market. The quantities traded in foreign exchange markets are breathtaking. A 2019 Bank of International Settlements survey found that $5.3 trillion per day was traded on foreign exchange markets, which makes the foreign exchange market the largest market in the world economy. In contrast, 2019 U.S. real GDP was $21.4 trillion per year.

Your transaction is simple enough. Suppose you carry a $100 bill. You bring it into the foreign currency office and look up, and you see a bunch of different numbers on a digital board. For example, if you are traveling to Turkey, whose national currency is the Turkish Lira, one line of the board might read: “U.S. DOLLARS: BUY 5.50; SELL 5.80.” This means that the office will give you 5.50 Turkish Lira in exchange for 1 U.S. dollar. If you have $100, the office will give you 550 Turkish Lira. If you want to sell Turkish Lira for U.S. dollars, the office will surely buy them from you, but not at the same exchange rate, since the office will make some money on the exchange. So if you bring 550 Turkish Lira and ask for U.S. dollars, it will not give you 100 dollars, but instead about $95. The important point is that this one transaction, when repeated all over the world for all sorts of different transactions, ends up totaling $6.6 trillion worth of exchanges per day.

Table 29.1 shows the currencies most commonly traded on foreign exchange markets. The U.S. dollar dominates the foreign exchange market, being on one side of 88.3% of all foreign exchange transactions. The U.S. dollar is followed by the euro, the British pound, the Australian dollar, and the Japanese yen.