The invention relates to an overspeed detection mechanism in lift apparatuses, safety device acting against overspeed and a lift apparatus, which detection mechanism can be assembled on a sheave (50, 50') or on the elevator car (3). It incorporates a wheel (13) rotating according to the speed of the car (3) and has pivoting arms (20, 21) swinging through the centrifugal force during the rotation of the wheel (13). It has magnetic means associated to the pivoting arms (20, 21) causing an attraction maintaining the position of the pivoting arms (20, 21) until the centrifugal force exceeds the attraction of the magnetic means. It incorporates a stop (30), belonging to a part (11-11') external to the wheel (13) against which the pivoting arm (20, 21) comes into contact when the centrifugal force generated on the pivoting arm (20, 21) due to the overspeed of the elevator car (3) exceeds the attractive force of the magnetic means, starting the braking of the car (3).
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