  A general class of gauges for open string field theory, for which the gauge
fixing condition is given by linear equations with respect to string field, is
investigated in detail. This class of gauges includes almost all known ones
like Siegel gauge and its various extensions such as a-gauges proposed by the
present authors as well as Schnabl gauge and linear b-gauges. A general form of
propagators is determined and their common features are analyzed. A consistent
procedure for calculating the amplitudes is given. Gauge independence of the
on-shell physical amplitudes is explicitly shown.
