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.