PURPOSE: To effectively cut off oscillation energy from a power unit system by interposing a resilient body between the rising wall of a rear mount member and a member at the side of the power unit.

CONSTITUTION: A rubber vibration insulator 14 is molded in such a form that it may catch a rear mount member 8 in the lengthwise direction of a car by use of the space of rising walls of the rear mount member 8 so as to resist to the upward and downward force from a power unit 1 by the shearing strength thereof. The room for placing a rubber vibration insulator 14 between the unit 1 and the member 8 may be therefore minimized and in addition, a spring constant high enough to provide for sufficient vibration insulating effect is secured. The position at which the member 8 for supporting the rubber vibration insulator 14 is fitted to the car body is allowed to be set at a part having high rigidity in the vicinity of a tunnel part 6a of a floor panel 6 so that vibration of the unit 1 may be effectively shielded.