Abstract: A detecting and protecting device includes detecting devices, and an ultrasonic sensor; the detecting devices are connected to respective ones of expanding assemblies of a shrink film machine, and each include a seat behind a supporting rod of a corresponding expanding assembly, a movable rod passed through the seat and projecting below the supporting rod, a stopping board pivoted to one end of the movable rod, a shading block joined to one end of the stopping board, and a sensor positioned on the movable rod and normally shaded by the shading block; if the stopping board comes into contact with goods while a shrink film is being lowered, it will tilt, and the shading block will no longer shade the sensor; the ultrasonic sensor is used for measuring height of the goods such that sealing and cutting action will start immediately after the film encompasses the goods.