A parallel hybrid power transmission mechanism comprising: an engine; a crank shaft disposed on the engine; a motor generator; a driven device to which a power of the engine and/or the motor generator is transmitted; an input shaft disposed on the driven device; a flywheel connected to the crank shaft and configured to be rotated; a rotor disposed on the motor generator, including a first connecting portion connected to an outside of the flywheel in a radial direction, the rotor being configured to supply and receive a rotational force to and from the flywheel through the first connecting portion; a coupling arranged independently from the rotor, including a second connecting portion connected to an inside of the flywheel in the radial direction, the coupling being configured to receive the rotational force of the flywheel through the second connecting portion; and an intermediate shaft connecting the coupling and the input shaft to each other, the intermediate shaft being configured to transmit the rotational force received by the coupling to the input shaft characterized in that the coupling includes: a hub formed of flexible material and connected to the intermediate shaft; and a disk formed of rigid material, the disk protruding from the hub outwardly in the radial direction and including the second connecting portion connected to the flywheel, the rotor has a rotor boss having a hollow shape, the flywheel has a first concave portion on the rotor boss side, the rotor boss is arranged on an outside of the intermediate shaft in the radial direction between the rotor boss and the flywheel, and has a second concave portion on the flywheel side, and the hub of the coupling is arranged between the first concave portion and the second concave portion. an engine; a crank shaft disposed on the engine; a motor generator; a driven device to which a power of the engine and/or the motor generator is transmitted; an input shaft disposed on the driven device; a flywheel connected to the crank shaft and configured to be rotated; a rotor disposed on the motor generator, including a first connecting portion connected to an outside of the flywheel in a radial direction, the rotor being configured to supply and receive a rotational force to and from the flywheel through the first connecting portion; a coupling arranged independently from the rotor, including a second connecting portion connected to an inside of the flywheel in the radial direction, the coupling being configured to receive the rotational force of the flywheel through the second connecting portion; and an intermediate shaft connecting the coupling and the input shaft to each other, the intermediate shaft being configured to transmit the rotational force received by the coupling to the input shaft characterized in that the coupling includes: a hub formed of flexible material and connected to the intermediate shaft; and a disk formed of rigid material, the disk protruding from the hub outwardly in the radial direction and including the second connecting portion connected to the flywheel, a hub formed of flexible material and connected to the intermediate shaft; and a disk formed of rigid material, the disk protruding from the hub outwardly in the radial direction and including the second connecting portion connected to the flywheel, the rotor has a rotor boss having a hollow shape, the flywheel has a first concave portion on the rotor boss side, the rotor boss is arranged on an outside of the intermediate shaft in the radial direction between the rotor boss and the flywheel, and has a second concave portion on the flywheel side, and the hub of the coupling is arranged between the first concave portion and the second concave portion.