In data transfer in isochronous mode using an IEEE1394 serial bus, the data transfer rate is guaranteed, but data transfer is disabled if the number of channels is insufficient. The device has a network communication port for establishing communication with a network via a pre-defined protocol and communication mode, and has a camera communication port such as a serial, parallel, SCSI, USB or Irda-port that imitates the back end application of a PC, for connection to a digital camera for sending and receiving data to and from the camera. The joint portion includes a main frame fixed to the head unit. The end packing elements are provided with an annular packing member extending around the shaft and including a front face, which is directed towards said sealing surface and which is in contact with the sealing surface or separated from the sealing surface by a gap constituting an axially directed narrow slot.