  We analyze the temporal variation of the diurnal anisotropy of sub-TeV cosmic
ray intensity observed with the Matsushiro (Japan) underground muon detector
over two full solar activity cycles in 1985-2008. The average sidereal
amplitude over the entire period is 0.034+-0.003 %, which is roughly one third
of the amplitude reported from AS and deep-underground muon experiments
monitoring multi-TeV GCR intensity suggesting a significant attenuation of the
anisotropy due to the solar modulation. We find, on the other hand, only weak
correlations either with the solar activity- or magnetic-cycles. We examine the
temporal variation of the "single-band valley depth" (SBVD) quoted by the
Milagro experiment and, by contrast with recent Milagro reports, we find no
steady increase in the Matsushiro observations in a 7-year period between 2000
and 2007. We suggest, therefore, that the steady increase of the SBVD reported
by the Milagro experiment is not caused by the decreasing solar modulation in
the declining phase of the 23rd solar activity cycle.
