The present invention relates to a device for preventing sudden acceleration of an automobile that is installed in a power transmission structure disposed between a throttle valve and a motor for the throttle valve in the automobile, such that if the motor is activated by an electrical error at a state where an accelerator pedal is not depressed by a driver, the power generated from the motor is not transmitted to the throttle valve. The device for preventing sudden acceleration of an automobile fitted with an automatic transmission according to the present invention is configured wherein even though a motor opening and closing a throttle valve is activated by an electrical error at a state where an accelerator pedal is not depressed by a driver, the power generated from the motor is not transmitted mechanically to the throttle valve, thereby preventing casualty caused by sudden acceleration.