A power transmission device comprising: a clutch housing that is rotatable together with an input member that is rotatable by a drive force of an engine of a vehicle, a plurality of driving clutch plates being attached to the clutch housing; a clutch member coupled to an output member that can rotate a wheel of the vehicle, a plurality of driven clutch plates formed alternately with the driving clutch plates of the clutch housing being attached to the clutch member; a pressure member that is movable between an actuation position, at which the drive force of the engine can be transmitted to the wheel with the driving clutch plates and the driven clutch plates brought into press contact with each other, and a non-actuation position, at which transmission of the drive force of the engine to the wheel can be blocked by releasing a press-contact force between the driving clutch plates and the driven clutch plates; a weight member disposed in a groove portion provided in the clutch housing to extend in a radial direction, the weight member being movable from a radially inner position to a radially outer position of the groove portion by a centrifugal force due to rotation of the clutch housing; an interlocking member that can move the pressure member from the non-actuation position to the actuation position as the weight member is moved from the radially inner position to the radially outer position; a first clutch member coupled to the output member; a second clutch member to which the driven clutch plates are attached; and a back torque transmission cam, characterized in that the back torque transmission cam can bring the driving clutch plates and the driven clutch plates into press contact with each other by moving the second clutch member when the pressure member is located at the non-actuation position and a rotational force is input to the first clutch member via the output member, and a torque transmission portion formed on each of the first clutch member and the second clutch member to be able to transmit a rotational force transmitted to the second clutch member to the first clutch member not via the back torque transmission cam. a clutch housing that is rotatable together with an input member that is rotatable by a drive force of an engine of a vehicle, a plurality of driving clutch plates being attached to the clutch housing; a clutch member coupled to an output member that can rotate a wheel of the vehicle, a plurality of driven clutch plates formed alternately with the driving clutch plates of the clutch housing being attached to the clutch member; a pressure member that is movable between an actuation position, at which the drive force of the engine can be transmitted to the wheel with the driving clutch plates and the driven clutch plates brought into press contact with each other, and a non-actuation position, at which transmission of the drive force of the engine to the wheel can be blocked by releasing a press-contact force between the driving clutch plates and the driven clutch plates; a weight member disposed in a groove portion provided in the clutch housing to extend in a radial direction, the weight member being movable from a radially inner position to a radially outer position of the groove portion by a centrifugal force due to rotation of the clutch housing; an interlocking member that can move the pressure member from the non-actuation position to the actuation position as the weight member is moved from the radially inner position to the radially outer position; a first clutch member coupled to the output member; a second clutch member to which the driven clutch plates are attached; and a back torque transmission cam, characterized in that the back torque transmission cam can bring the driving clutch plates and the driven clutch plates into press contact with each other by moving the second clutch member when the pressure member is located at the non-actuation position and a rotational force is input to the first clutch member via the output member, and a torque transmission portion formed on each of the first clutch member and the second clutch member to be able to transmit a rotational force transmitted to the second clutch member to the first clutch member not via the back torque transmission cam.