  The data from a CO(1 - 0) mapping survey of 40 nearby spiral galaxies
performed with the Nobeyama 45-m telescope are presented. The criteria of the
sample selection were (1) RC3 morphological type in the range Sa to Scd, (2)
distance less than 25 Mpc, (3) inclination angle less than 79deg (RC3), (4)
flux at 100 um higher than ~ 10 Jy, (5) spiral structure is not destroyed by
interaction. The maps of CO cover most of the optical disk of the galaxies. We
investigated the influence of bar on the distribution of molecular gas in
spiral galaxies using these data. We confirmed that the degree of central
concentration is higher in barred spirals than in non-barred spirals as shown
by the previous works. Furthermore, we present an observational evidence that
bars are efficient in driving molecular gas that lies within the bar length
toward the center, while the role in bringing gas in from the outer parts of
the disks is small. The transported gas accounts for about half of molecular
gas within the central region in barred spiral galaxies. We found a correlation
between the degree of central concentration and bar strength. Galaxies with
stronger bars tend to have higher central concentration. The correlation
implies that stronger bars accumulate molecular gas toward the center more
efficiently. These results are consistent with long-lived bars.
