A rotation transmission device built in as a drive unit of a rotating machine suitable for operation of a ventilation opening / closing system is provided. A torsion coil spring (11) is installed inside a cylinder of a brake drum (10) so that an outer diameter surface is in contact with an inner peripheral surface of the brake drum (10), and driven end portions (11a) at both ends of the coil spring (11) are radially inward. It is curved in a semicircular shape facing toward the side and facing in the circumferential direction. The input shaft 12 and the output shaft 13 are disposed so as to be rotatable relative to both end portions of the shaft pin 14, and the rotation transmission portion 12 c protruding from the respective inner end portions in a direction parallel to the shaft pin 14 and the rotated shaft With respect to the driven end portion 11 a of the torsion coil spring 11, the transmission portion 13 c causes the rotation transmission portion 12 c of the input shaft 12 to contact the semicircular inner peripheral side to reduce the diameter of the coil spring 11, thereby rotating the output shaft 13. The transmission portion 13c hits the semicircular outer peripheral side and expands the coil spring 11 in diameter. [Selection] Figure 2【課題】換気用開閉システムの操作に好適な回転機の駆動部として内蔵される回転伝達装置を提供する。【解決手段】制動ドラム１０の筒内部に、捻りコイルバネ１１が、外径面を制動ドラム１０の内周面に接する状態に設置され、該コイルバネ１１の両端の被駆動端部１１ａは半径方向内方側へ、且つ円周方向に相対峙する向きの半円形状に湾曲されている。入力軸１２と出力軸１３は軸ピン１４の両端部に、回転自在に相対峙する配置とされ、それぞれの内端部から軸ピン１４と平行する方向に突き出された回転伝達部１２ｃと被回転伝達部１３ｃは、捻りコイルバネ１１の被駆動端部１１ａに対して、入力軸１２の回転伝達部１２ｃは半円形状の内周側へ当たってコイルバネ１１を縮径させ、出力軸１３の被回転伝達部１３ｃは前記半円形状の外周側へ当たってコイルバネ１１を拡径させる。【選択図】図２
