The invention relates to a fastening device (1) of a penis extension device with a coupling element (5) for exerting a tensile force on a penis and with a tensile force meter (7,8,19,27) which is characterized in that a first electronics component (9) and a first current source (10) are present, the tensile force meter (7,8, 19,27) electrically or electronically determines the measurement value for the exerted tension together with the first electronics component (9), and the first electronics component (9) has a first radio device for transmitting the determined measurement value to an external receiver. With this device it is possible for a relevant measurement value, in particular the measurement value for the exerted tensile force, to be transmitted from the sensitive area in which the fastening device according to the invention is used to an external device, for example to an app of a cell phone.
