  We present high-resolution (~ 4") 12CO (J = 1 - 0) mapping observations with
high - velocity resolution (~ 2.6 km s^{-1}) toward the disk of flocculent
galaxy NGC 5055, using the Nobeyama Millimeter Array in order to study the
physical properties of the molecular clouds in the arm and the interarm. The
obtained map shows clumpy structures. Although these are mainly distributed
along a spiral arm seen in near-infrared observations, some clouds are located
far from the arm, namely in the interarm. These clouds in both the arm and the
interarm have a typical size and mass of a few 100 pc and a few 10^6 Mo,
respectively. These correspond to the largest Giant Molecular Cloud (GMC) in
our Galaxy, and are slightly smaller than Giant Molecular Associations (GMAs)
in the grand design spiral M 51. Their CO flux-based masses show good agreement
with their virial masses. A size - velocity dispersion relation is also plotted
on an extension of the relation for the Galactic GMCs. These facts suggest that
the properties of these clouds are similar to that of the Galactic GMCs. We
also found no clear systematic offset between the molecular gas and HII regions
unlike M 51. This fact and no existense of GMAs suggest the view that, in NGC
5055, cloud formation and following star formation in both the arm and the
interarm are due to enhancement of gas by local fluctuation. On the other hand,
in grand design spiral galaxies, such as M 51, GMA formations may occur only in
the arm due to a strong density wave also enhanced star formation in GMA
formation may also occur. These may control the optical morphology of spiral
arms in spiral galaxies.
