  We conduct a systematic study of galactic outflows in star-forming galaxies
at $z\sim0$-$2$ based on the absorption lines of optical spectra taken from
SDSS DR7, DEEP2 DR4, and Keck Erb et al. We carefully make stacked spectra of
homogeneous galaxy samples with similar stellar mass distributions at
$z\sim0$-$2$, and perform the multi-component fitting of model absorption lines
and stellar continua to the stacked spectra. We obtain the maximum
($v_\rm{max}$) and central ($v_\rm{out}$) outflow velocities, and estimate the
mass loading factors ($\eta$), a ratio of the mass outflow rate to the star
formation rate (SFR). Investigating the redshift evolution of the outflow
velocities measured with the absorption lines whose depths and ionization
energies are similar (Na I D and Mg I at $z\sim0$-$1$; Mg II and C II at
$z\sim1$-$2$), we identify, for the first time, that the average value of
$v_\rm{max}$ ($v_\rm{out}$) significantly increases by 0.05-0.3 dex from
$z\sim0$ to $2$ at a given SFR. Moreover, we find that the value of $\eta$
increases from $z\sim0$ to $2$ by $\eta \propto (1 + z)^{1.2\pm0.3}$ at a given
halo circular velocity $v_\rm{cir}$ , albeit with a potential systematics
caused by model parameter choices. The redshift evolution of $v_\rm{max}$
($v_\rm{out}$) and $\eta$ is consistent with the galaxy-size evolution and the
local velocity-SFR surface density relation, and explained by high-gas
fractions in high-redshift massive galaxies, which is supported by recent radio
observations. We obtain a scaling relation of $\eta \propto v_\rm{cir}^a$ for
$a = -0.2 \pm 1.1$ in our $z\sim0$ galaxies that agrees with the
momentum-driven outflow model ($a = -1$) within the uncertainty.
