COUPLING

A flexible unit absorbing misalignment and transmitting torque from a driving shaft to a driven shaft is provided between a pair of flanges individually provided on each of the driving shaft side and the driven shaft side, both the driving shaft and the driven shaft being hollow. A communication passage letting hollow regions of the driving shaft and the driven shaft communicate with each other to form a circulation space for a cooling fluid is provided in the flexible unit. The flow of the cooling fluid cooling a driving source driving and rotating the driving shaft from the inside is created in the circulation space. A seal portion seals between the circulation space and an outside space to prevent leakage of the cooling fluid from the circulation space to the outside space.