  The formation of molecular clouds out of HI gas is the first step toward star
formation. Its metallicity dependence plays a key role to determine star
formation through the cosmic history. Previous theoretical studies with
detailed chemical networks calculate thermal equilibrium states and/or thermal
evolution under one-zone collapsing background. The molecular cloud formation
in reality, however, involves supersonic flows, and thus resolving the cloud
internal turbulence/density structure in three dimension is still essential. We
here perform magnetohydrodynamics simulations of 20 km s^-1 converging flows of
Warm Neutral Medium (WNM) with 1 micro Gauss mean magnetic field in the
metallicity range from the Solar (1.0 Zsun) to 0.2 Zsun environment. The Cold
Neutral Medium (CNM) clumps form faster with higher metallicity due to more
efficient cooling. Meanwhile, their mass functions commonly follow dn/dm
proportional to m^-1.7 at three cooling times regardless of the metallicity.
Their total turbulence power also commonly shows the Kolmogorov spectrum with
its 80 percent in the solenoidal mode, while the CNM volume alone indicates the
transition towards the Larson's law. These similarities measured at the same
time in the unit of the cooling time suggest that the molecular cloud formation
directly from the WNM alone requires a longer physical time in a lower
metallicity environment in the 1.0--0.2 Zsun range. To explain the rapid
formation of molecular clouds and subsequent massive star formation possibly
within less than 10 Myr as observed in the Large/Small Magellanic Clouds
(LMC/SMC), the HI gas already contains CNM volume instead of pure WNM.
