The invention provides a torsional vibration reducing device, which can reduce the abnormal voice generated by collision between a rolling body and a rolling chamber and is capable of reducing protruded cracks in a heat treatment. A protrusion (70) is configured to be closer to the rotation direction of a plate (50), compared with a straight line (L2) that penetrates the center of a rolling body (46) and the plate (50); the center of the rolling body (46) is: the center of the rolling body (46), when the rolling body (46) in the middle of a rolling room (48), and the rolling body (46) can swing to two ends of the rolling room (48); thus, compared with the situation that the protrusion (70) is arranged on the straight line (L1), the angle (theta2) of the top end of the protrusion (70) is enlarged; thus during a heat treatment for enhancing the hardness of the protrusion (70) for manufacturing of the plate (50), the cracking of the protrusion (70) is inhibited; and thus the quality of the plate (50) is improved.