  We present the results of SiO line observations of a sample of known SiO
maser sources covering a wide dust-temperature range. The aim of the present
research is to investigate the causes of the correlation between infrared
colors and SiO maser intensity ratios among different transition lines. We
observed in total 75 SiO maser sources with the Nobeyama 45m telescope
quasi-simultaneously in the SiO J=1-0 v=0, 1, 2, 3, 4 and J=2-1 v=1, 2 lines.
We also observed the sample in the 29SiO J=1-0 v=0 and J=2-1 v=0, and 30SiO
J=1-0 v=0 lines, and the H2O 6(1,6)-5(2,3) line. As reported in previous
papers, we confirmed that the intensity ratios of the SiO J=1-0 v=2 to v=1
lines clearly correlate with infrared colors. In addition, we found possible
correlation between infrared colors and the intensity ratios of the SiO J=1-0
v=3 to v=1&2 lines.
