PROBLEM TO BE SOLVED: To provide an electromagnetic brake which can reduce noise such as a collision sound generated by a collision between an armature and a yoke or a disk, or a sliding sound and a squeaky sound between the armature and the disk, and an electronic clutch. SOLUTION: An electromagnetic brake 20A comprises a disk 22 rotating integrally with a braked rotary shaft 2, a yoke 23 arranged at one side of the disk 22, an armature 24 arranged movably in the axial direction and unrotatably between the disk 22 and the yoke 23, and a plate 25 fixed to the yoke 23 by sandwiching the disk 22 and the armature 24 between a space with the yoke 23. Furthermore, in the disk 22, a resonance structure 30 reducing a sound generated when the disk 22 collides with the armature 24 is formed. Additionally, the resonance structure 30 is composed of a small-diameter hole 31 having an opening connected to an external space at the armature 24 side, and a large-diameter hole 32 having an opening at only the small-diameter hole side. COPYRIGHT: (C)2009,JPO&INPIT