A power transmission device disposed in a path from a drive source to a wheel in a vehicle is disclosed. The power transmission device includes an input-side rotary member, an output-side rotary member, and a magnetic damper mechanism. A torque is inputted from the drive source to the input-side rotary member. The output-side rotary member is disposed to be rotatable relative to the input-side rotary member. The magnetic damper mechanism is configured to elastically couple the input-side rotary member and the output-side rotary member in a rotational direction by a magnetic force of attraction. The magnetic damper mechanism has a variable stiffness.