The present invention has an object to provide a control method and a control
apparatus for a variable wavelength optical filter, which can reliably and stably
control drive conditions of the variable wavelength optical filter, independent
of the number of wavelengths to be selectively separated in collective. To this
end, the control apparatus for a variable wavelength optical filter according to
the present invention comprises: a light reception section that takes out to receive,
in collective, monitor light corresponding to each optical signal selectively separated
by the variable wavelength optical filter, and creates a monitor signal a level
of which is changed corresponding to the power of the received monitor light; an
alternating current component extraction section that extracts an alternating current
component of the monitor signal generated by the light reception section; and a
tracking control section that controls the drive condition of the variable wavelength
optical filter based on a level change in the alternating current component extracted
by the alternating current component extraction section.