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A natural monopoly is a monopoly in an industry in which it is most efficient (involving the lowest long-run average cost) for production to be permanently concentrated in a single firm rather than contested competitively. This market situation gives the largest supplier in an industry, often the first supplier in a market, an overwhelming cost advantage over other actual and potential competitors, so a natural monopoly situation generally leads to an actual monopoly. This tends to be the case in industries where capital costs predominate, creating economies of scale that are large in relation to the size of the market, and hence creating high barriers to entry; examples include public utilities such as water services and electricity.〔Perloff, J, 2012. Microeconomics, Pearson Education, England, p. 394.〕 While in other situations a monopoly can lead to restricted output, higher-than-necessary prices, and production that is inefficient (at higher average cost) than would occur with many producers, a firm that is a natural monopoly produces at lower average cost than would be possible with multiple firms. This frees other potential competitors to put their resources to other profitable uses.〔Competitive Enterprise Institute. The Problem with Predation. http://cei.org/news-letters-cei-planet/problem-predation. webpage. 4/22/14〕 == Definition == Two different types of cost are important in microeconomics: marginal cost, and fixed cost. The marginal cost is the cost to the company of serving one more customer. In an industry where a natural monopoly does not exist, the vast majority of industries, the marginal cost decreases with economies of scale, then increases as the company has growing pains (overworking its employees, bureaucracy, inefficiencies, etc.). Along with this, the average cost of its products decreases and increases. A natural monopoly has a very different cost structure. A natural monopoly has a high fixed cost for a product that does not depend on output, but its marginal cost of producing one more good is roughly constant, and small. All industries have costs associated with entering them. Often, a large portion of these costs is required for investment. Larger industries, like utilities, require enormous initial investment. This barrier to entry reduces the number of possible entrants into the industry regardless of the earning of the corporations within. Natural monopolies arise where the largest supplier in an industry, often the first supplier in a market, has an overwhelming cost advantage over other actual or potential competitors; this tends to be the case in industries where fixed costs predominate, creating economies of scale that are large in relation to the size of the market, as is the case in water and electricity services. The fixed cost of constructing a competing transmission network is so high, and the marginal cost of transmission for the incumbent so low, that it effectively bars potential competitors from the monopolist's market, acting as an early insurmountable barrier to entry into the market place. A firm with high fixed costs requires a large number of customers in order to have a meaningful return on investment. This is where economies of scale become important. Since each firm has large initial costs, as the firm gains market share and increases its output the fixed cost (what they initially invested) is divided among a larger number of customers. Therefore, in industries with large initial investment requirements, average total cost declines as output increases over a much larger range of output levels. Companies that take advantage of economies of scale often run into problems of bureaucracy; these factors interact to produce an "ideal" size for a company, at which the company's average cost of production is minimized. If that ideal size is large enough to supply the whole market, then that market is a natural monopoly. Once a natural monopoly has been established because of the large initial cost and that, according to the rule of economies of scale, the larger corporation (to a point) has lower average cost and therefore a huge advantage. With this knowledge, no firms attempt to enter the industry and an oligopoly or monopoly develops. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Natural monopoly」の詳細全文を読む スポンサード リンク
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