A torsional vibration reducing device comprising: a rotating body configured to rotate when torque is input to the rotating body; an inertial body configured to rotate relative to the rotating body so as to suppress torsional vibration of the rotating body when the torque fluctuates; a coupling member configured to transmit the torque to the rotating body and to the inertial body; a first coupling portion provided to one of the rotating body and the inertial body, the first coupling portion engaging with the coupling member such that the first coupling portion restricts movement of the coupling member in a rotational direction of the rotating body and allows movement of the coupling member in a radial direction of the rotating body; and a second coupling portion provided to another one of the rotating body and the inertial body, the second coupling portion engaging with the coupling member such that when the rotating body and the inertial body rotate relative to each other, a contact portion of the coupling member with respect to the first coupling portion moves in the radial direction of the rotating body, wherein the first coupling portion extends in the radial direction of the rotating body, and the first coupling portion includes a guide groove portion, the guide groove portion sandwiches the coupling member so as to guide the coupling member in the radial direction of the rotating body, a surface, that contacts the guide groove portion, of the coupling member is a curved surface, the coupling member is a swing body that rotates about a portion offset from a center of curvature of the curved surface, characterised in that the second coupling portion includes a coupling pin that is fitted to the swing body so as to rotate at a rotation center of the swing body. a rotating body configured to rotate when torque is input to the rotating body; an inertial body configured to rotate relative to the rotating body so as to suppress torsional vibration of the rotating body when the torque fluctuates; a coupling member configured to transmit the torque to the rotating body and to the inertial body; a first coupling portion provided to one of the rotating body and the inertial body, the first coupling portion engaging with the coupling member such that the first coupling portion restricts movement of the coupling member in a rotational direction of the rotating body and allows movement of the coupling member in a radial direction of the rotating body; and a second coupling portion provided to another one of the rotating body and the inertial body, the second coupling portion engaging with the coupling member such that when the rotating body and the inertial body rotate relative to each other, a contact portion of the coupling member with respect to the first coupling portion moves in the radial direction of the rotating body, wherein the first coupling portion extends in the radial direction of the rotating body, and the first coupling portion includes a guide groove portion, the guide groove portion sandwiches the coupling member so as to guide the coupling member in the radial direction of the rotating body, a surface, that contacts the guide groove portion, of the coupling member is a curved surface, the coupling member is a swing body that rotates about a portion offset from a center of curvature of the curved surface, characterised in that the second coupling portion includes a coupling pin that is fitted to the swing body so as to rotate at a rotation center of the swing body.