A dynamic damper capable of reducing vibration of a support where an exhaust collecting tube of a diesel engine is mounted. The dynamic damper has a tubular case (2), a guide bar (5) provided in the case (2), weights (9a) for vibration suppression slidably fitted on the guide bar (5), a pair of coil springs (10) arranged on both sides of the weights (9a), a pair of guide bar support bodies (3a, 3b) arranged at both ends of the case (2), a weight (9b) for adjusting natural vibration frequency, provided between each of the guide bar support bodies (3a, 3b) and each of the coil springs (10), fasteners (6) screwed to both ends of the guide bar (5), and support members (22, 23) arranged on side faces of the case (2).