A device and a method for detecting elevator rope elongation, and an elevator. An elevator rope is connected to a rope head device and an operating device in an elevator, and the device for detecting elevator rope elongation includes: one and more brackets connected to an elastic reset member in the rope head device, a coupling member connected to at least one of the brackets and configured to be driven into a trigger position by the at least one bracket when the displacement of the elastic reset member exceeds a threshold value due to reduction of compression amount, and a trigger connected to the coupling member and configured to be triggered to generate a trigger signal when the coupling member is driven into the trigger position.