To extremely facilitate optimization adjustment of damping rate.

This device is provided with a discord piston 3 coaxially provided on a rotary shaft 2 accompanying longitudinal vibration, two oil chambers 5, 6, oil passages 7, 8, 9 communicating between the oil chambers, and a damper mechanism damping longitudinal vibration of the rotary shaft transmitted from the piston to damper oil. The damper mechanism is provided with a cylinder part 22 provided in an axial line direction with including a round section shape inner circumference part formed in a tapered shape extending in the axial line direction, a piston part 23 including an outer circumference part formed in a round section shape tapered shape extending in the axial line direction and provided in the cylinder part in the axial line direction to form a clearance 26 for making damper oil pass therethrough with operating together with the cylinder part, a piston movement part 24 for moving the piston part, and a clearance width adjusting mechanism 25 for adjusting clearance width by changing an axial direction fixing position of the piston part from an outside.