A power transmission device includes an input rotary member, an intermediate rotary member, an output rotary member, a friction engaging part and a load adjusting mechanism. A torque is inputted to the input rotary member. The torque is inputted from the input rotary member to the intermediate rotary member. The torque is outputted from the output rotary member. The friction engaging part is engaged by friction with a friction force depending on a load applied thereto. The friction engaging part is configured to transmit the torque between the intermediate rotary member and the output rotary member. The load adjusting mechanism is configured to adjust the load applied to the friction engaging part in accordance with the torque inputted to the input rotary member.