Disclosed is an extension apparatus for enlarging and straightening a penis. The extension apparatus includes a fastening device (1) that is mounted on the penis, and a tension device (8) which is connected to the fastening device (1). The fastening device is provided with a dimensionally stable receiving member (2) which positively accommodates the entire area of the glans penis and whose inner contour essentially matches the shape of the glans penis. The fastening device can be connected to a device for supplying and sucking air and adjoins an elastic tubular seal (15) at the opening (3) provided for introducing the glans penis. The simple apparatus, which is suitable also for short penis lengths, can be put on quickly and in an uncomplicated manner, provides a high degree of comfort during wearing and optimum tensile strength, resulting in a gentle extension treatment that has no major side effects for the user.
