To provide a power unit having an internal-combustion engine, provided with a vibration resistant mechanism capable of showing an effective damping effect on a plurality of or a wide frequency range of vibration in a simple structure.

A mass housing 32 having mass accommodating space 34 is fixed to an unit block 20. The position of the mass housing 32 is also set up to be closer to an outward edge portion of the unit block 20 than the center of gravity of the power unit in a projection to a horizontal surface. An independent mass member 36 having 1 to 5% of the mass of the power unit is accommodated and arranged in the mass accommodating space 34 and also enables relative displacement to the mass housing 32 in a non-gluing state. The damping effect is performed in proportion to striking of the independent mass member 36 against the mass housing 32.