A fall arrester includes a holder, rotating drum, braking device, and dust cover. The rotating drum is pivotally provided on and within the holder, and includes a main body and at least one pawl; the main body has an accommodating part to be wound by a cable and a setting part. The pawl is pivotally provided on the setting part, and the braking device is fixed to the holder and between the holder and the setting part. When the rotating drum rotates quickly by pull of the cable, the pawl would pivot and make a part thereof abut against a part of the braking device to stop the rotating drum. The dust cover is fixed to the setting part, and thereby prevents dust from affecting the pawl and the braking device located therein, and thus to enhance safe use thereof.