A testing device for detecting a contact pressure of a vehicle side window contacting a window seal arranged on the bodywork. In order to provide a universally applicable testing device that can be used for different vehicle types and models and that allows for reliable determination of the contact pressures, the testing device is designed having a central processing unit comprising a power supply, an evaluation unit and a display unit for showing the determined contact pressure, and having a pressure measuring film that can be removably arranged on the vehicle side window in the region of the window seal and that is connected to the evaluation unit of the central processing unit.