An automatic alert device is provided for a suction cup, including a pump and a suction cup positionable on an object to be handled. The pump is operable to drive air out of the suction cup thereby inducing suction force on the object to be handled. When the suction cup gradually loses the suction force, a plunger of the pump gets moved out of the pump. When the outward movement of the plunger reaches a preset extent, the alert device that includes a warning light and an audio alert is activated to cause the warning light and the audio alert to give off warnings of light and sound respectively. Thus, an operator can be immediately notified of the situation of losing suction force for taking remedial operation to get the suction force back to the desired level.