An oscillation limiting mechanism 4 is integrally provided to an engine mount 3 (a vibration proof mount device) of a power plant P mounted on an automobile in a traverse mount fashion. Not only is a stopper metal member 40 in the shape of an inverted U letter disposed so as to cross over a mount body portion 30, but a stopper rubber 42 is formed so that it protrudes from the rear end of a casing of the mount body portion 30 toward the rear side of the vehicle body. Not only is a hollow portion 43 formed in the interior of the stopper rubber 42, but a metal core body 44 is also embedded in the stopper rubber 42 so as to be revolvable around an axis in the vehicle body traverse direction as if it were a link. With such a construction adopted, the stopper rubber 42 is shear-deformed in the vertical direction with comparative ease even in a state where it is brought into contact with the rear side leg portion 40c of a stopper metal member 40 and thereby receives a compressive force in the vehicle body longitudinal direction, and a dynamic spring constant of the mount 3 in the vertical direction does not rise so much even if the stopper acts in rapid acceleration or the like; therefore, enabling increase in surrounding sound in acceleration to be suppressed with a simple structure less of cost up while oscillation of the power plant P is limited in a similar way to that of a torque rod.