An electromagnetic clutch is provided with: a clutch hub which is connected to a shaft member (one of a pair of rotation members); a clutch housing which is connected to a hollow shaft (the other of a pair of rotation members); a rotor which is connected to the clutch housing; a main clutch (clutch member) which is disposed between the clutch hub and the clutch housing; and an electromagnet which operates the main clutch. An end surface of the clutch housing and an end surface of a core of the electromagnet are disposed to be opposed to each other with the rotor interposed therebetween in an axial direction.The end of the rotor in a side of the clutch housing is formed with an extension portion which extends to the clutch housing in the axial direction. An outer periphery of the clutch housing is connected to the extension portion through a connection portion. The connection portion is disposed outside the main clutch in a radial direction.