An electromagnetic clutch comprising: a first rotary member formed of a magnetic material; a second rotary member arranged in an axial portion of the first rotary member, and rotatable with respect to the first rotary member; an armature hub including a boss formed on one end portion of the second rotary member in an axial direction, and a flange extending outside in a radial direction from the boss; an armature formed into an annular shape including a hollow portion having a diameter larger than an outer diameter of the flange, and arranged in a position facing one end portion of the first rotary member in the axial direction, the flange being inserted into the hollow portion; a single leaf spring configured to connect the armature to the flange, and bias the armature away from the first rotary member by a spring force; an electromagnetic coil configured to generate a magnetic flux (Φ), and magnetically attract the armature to the first rotary member against the spring force of the leaf spring; a plurality of first rivets configured to fix the leaf spring to the flange; and a plurality of second rivets configured to fix the leaf spring to the armature, wherein the leaf spring includes a base formed into an annular shape, positioned on the same axis as that of the second rotary member, and overlaid on and fixed to the flange, a plurality of first through holes which are formed in the base, and into which the plurality of first rivets are inserted, respectively, a plurality of stoppers projecting outside in the radial direction from portions, in which the first plurality of through holes are formed, of an outer circumferential portion of the base and facing the armature in the axial direction, a plurality of connecting pieces each including a pair of connecting portions projecting outside in the radial direction from two sides of each of the plurality of stoppers on an outer circumferential portion of the base, and having distal ends connected to each other, a plurality of second through holes which are formed in projecting ends of the plurality of connecting pieces, respectively, and into which the plurality of second rivets are inserted, resceptively, a plurality of punched holes formed between the plurality of connecting pieces and the plurality of stoppers, respectively, outside the base in the radial direction, characterized by a plurality of low-strength portions formed in boundary portions between the base and the plurality of connecting portions and each having strength lower than that in a periphery of each of the plurality of first through holes, the boundary portions overlapping an outer circumferential edge of the flange when viewed in an axial direction of the second rotary member, wherein the leaf spring further includes a plurality of notches each formed in a portion adjacent to and inside each of the boundary portions in the radial direction, and each extending outside in the radial direction from an inner circumferential edge of the base, and the plurality of low-strength portions are sandwiched between the plurality of notches and the plurality of punched holes. a first rotary member formed of a magnetic material; a second rotary member arranged in an axial portion of the first rotary member, and rotatable with respect to the first rotary member; an armature hub including a boss formed on one end portion of the second rotary member in an axial direction, and a flange extending outside in a radial direction from the boss; an armature formed into an annular shape including a hollow portion having a diameter larger than an outer diameter of the flange, and arranged in a position facing one end portion of the first rotary member in the axial direction, the flange being inserted into the hollow portion; a single leaf spring configured to connect the armature to the flange, and bias the armature away from the first rotary member by a spring force; an electromagnetic coil configured to generate a magnetic flux (Φ), and magnetically attract the armature to the first rotary member against the spring force of the leaf spring; a plurality of first rivets configured to fix the leaf spring to the flange; and a plurality of second rivets configured to fix the leaf spring to the armature, wherein the leaf spring includes a base formed into an annular shape, positioned on the same axis as that of the second rotary member, and overlaid on and fixed to the flange, a plurality of first through holes which are formed in the base, and into which the plurality of first rivets are inserted, respectively, a plurality of stoppers projecting outside in the radial direction from portions, in which the first plurality of through holes are formed, of an outer circumferential portion of the base and facing the armature in the axial direction, a plurality of connecting pieces each including a pair of connecting portions projecting outside in the radial direction from two sides of each of the plurality of stoppers on an outer circumferential portion of the base, and having distal ends connected to each other, a plurality of second through holes which are formed in projecting ends of the plurality of connecting pieces, respectively, and into which the plurality of second rivets are inserted, resceptively, a plurality of punched holes formed between the plurality of connecting pieces and the plurality of stoppers, respectively, outside the base in the radial direction,