At the end of the seventeenth century, a new type of flute was invented. The new instrument, today known as the baroque flute, was significantly different from any type of flutes available in the previous periods. New elements to the flute included a seventh tone hole and a key that closes and opens the added tone hole. The key, called the E-flat key, played an important role in the develop-ment of the flute and the music written for it in the eighteenth century, since the intonation of the new instrument was, with the key, greatly improved over the older flutes. In addition, the fingering for some notes also became remarkably simpler, eliminating awkward fingerings such as those for E-flats/D-sharps and G-sharps/A-flats, which were produced through partly covering some of the tone holes.  Today, a baroque flute player can learn much about the use of the E-flat key from the treatises written in the eighteenth century. The information in the trea-tises, however, is not consistent. Some writers including Quantz and Hotteterre, the authors of the two most important eighteenth-century treatises, suggest us-ing the E-flat key as little as possible. Others, however, are much more open-minded, allowing a player to depress the key for those notes where the pitch is adversely affected. These discrepancies exist because each treatise writer had different views on the construction of the instrument, tone quality, and intonation. However, many baroque flute players today, especially those who perform on both modern and baroque flutes, tend to overuse the key, uniformly following the modern flute-playing method, in which the key is used to produce nearly all notes. This type of playing is disagreed not only by Quantz and Hotteterre but also by those treatise writers who allowed the frequent use of the key. To under- 134stand eighteenth-century music and flutes， today's players need to determine ex-actly how Quantz， Hotteterre， and others regarded the use of the key to avoidblindly imitating the modern flute-playing method. This paper examines the writ-ings of Quantz， Hotteterre， and others in detail to guide today's baroque fluteplayers in seeking the most appropriate way of using the key.はじめに右小指の運指に関する問題点楽器の特性と右小指の関係キーをバランス取りに使う欠点オトテールのキーに対する考え方クヴァンツの所見まとめ