A rotational fluctuation absorbing damper comprising: a hub; a pulley main body which is arranged concentrically with the hub and in a relatively rotatable state; and a coupling rubber which couples a side of the hub and a side of the pulley main body in such a manner as to be relatively displaceable in a circumferential direction, wherein a plurality of first projections are provided in the hub at predetermined intervals in a circumferential direction, a plurality of second projections are provided in the pulley main body at predetermined intervals in the circumferential direction while being positioned between the plurality of first projections, buffer portions positioned between the first projections and the second projections are formed in the coupling rubber, and characterized in that loosely fitted concave portions are provided between the respective buffer portions, each of the loosely fitted concave portions having a shape obtained by being hollowed out of the front surface side, the first projections and the second projections are accommodated in the loosely fitted concave portions in a loosely fitted state, in a free state, each of the first projections and the second projections exists at an intermediate position of the loosely fitted concave portion in the circumferential direction, and the first projections and the second projections are brought into contact with the buffer portions from both sides in the circumferential direction in the case that an amount of relative displacement in the circumferential direction of the hub and the pulley main body is equal to or more than a predetermined value. a hub; a pulley main body which is arranged concentrically with the hub and in a relatively rotatable state; and a coupling rubber which couples a side of the hub and a side of the pulley main body in such a manner as to be relatively displaceable in a circumferential direction, wherein a plurality of first projections are provided in the hub at predetermined intervals in a circumferential direction, a plurality of second projections are provided in the pulley main body at predetermined intervals in the circumferential direction while being positioned between the plurality of first projections, buffer portions positioned between the first projections and the second projections are formed in the coupling rubber, and characterized in that loosely fitted concave portions are provided between the respective buffer portions, each of the loosely fitted concave portions having a shape obtained by being hollowed out of the front surface side, the first projections and the second projections are accommodated in the loosely fitted concave portions in a loosely fitted state, in a free state, each of the first projections and the second projections exists at an intermediate position of the loosely fitted concave portion in the circumferential direction, and the first projections and the second projections are brought into contact with the buffer portions from both sides in the circumferential direction in the case that an amount of relative displacement in the circumferential direction of the hub and the pulley main body is equal to or more than a predetermined value.