A playback apparatus not only plays back an AV stream recorded on a BD-ROM but also downloads an update kit from a WWW server and writes it on a local HD. The outlet chamber includes an outlet for draining liquid out of the reservoir. The base plate is centrally provided at an upper surface thereof with a plurality of coupling protrusions in order to couple a second PCB, a ring-shaped washer, a rotation key, and a contact plate, to the base plate. A torque applied to the tool interface region will rotate the fastener head insert within the bore and cause the second set of protrusions to engage with the first set of protrusions to transfer torque to the fastener body. Assuming that the axial length of the contact carrier is 1, the first height x and the second height y satisfies a relationship given by the following expressions -: 0.