The teachings presented herein disclose a method and apparatus for controlling the optical power of a laser in a passive optical network transmitter that outputs a modulated optical signal responsive to a modulated input signal. There exists, in optical paths of the first optical system and the second optical system, a common optical element with a plurality of optical surfaces including refractive surfaces and reflective surfaces formed on a same medium and the first optical system and the second optical system share a part of optical surfaces of that optical element. With an inner surface of the display board lying on an outerface of the cover coupling to the framework to merely provide for support against vertical downward movement of the display board can be sufficient. Automatically generating external requests improves convenience for players, especially when inviting several other players to a voice chat session, because they do not have to find external contact information for each player who is not logged in. The pores may be arranged in a honeycomb arrangement or a rectangular array. Thus, it is possible to prevent image degradation by the gamma ray scattering in the radiation detector.