Abstract: An apparatus for detecting a strength of lips-closing is applied for training and evaluation during treatment of temporomandibular disorders (TMD), according to the strength of the lips-closing of the user, the clinical staff and the patients are able to evaluate the severity of lips-closing impairment. It can also be used as training tool with which the effect can be monitored before, during, and after rehabilitation courses. The apparatus includes an air bag, a pressure sensing unit and a micro-controller module. The user puts the air bag, which is able to be pumped air in or out, between the lips. The pressure sensing unit is connected to the air bag for detecting a pressure formed by the lips of the user forcing the air bag, to generate a signal. The micro-controller module is electrically connected to the pressure sensing unit for converting the signal into the strength of lips-closing.