  We present the results of Spectral Energy Distribution(SED) fitting analysis
for Lyman Break Galaxies(LBGs) at z~5 in the GOODS-N and its flanking fields
(the GOODS-FF). With the publicly available IRAC images in the GOODS-N and IRAC
data in the GOODS-FF, we constructed the rest-frame UV to optical SEDs for a
large sample (~100) of UV-selected galaxies at z~5. Comparing the observed SEDs
with model SEDs generated with a population synthesis code, we derived a
best-fit set of parameters (stellar mass, age, color excess, and star formation
rate) for each of sample LBGs. The derived stellar masses range from 10^8 to
10^11M_sun with a median value of 4.1x10^9M_sun. The comparison with z=2-3 LBGs
shows that the stellar masses of z~5 LBGs are systematically smaller by a
factor of 3-4 than those of z=2-3 LBGs in a similar rest-frame UV luminosity
range. The star formation ages are relatively younger than those of the z=2-3
LBGs. We also compared the results for our sample with other studies for the
z=5-6 galaxies. Although there seem to be similarities and differences in the
properties, we could not conclude its significance. We also derived a stellar
mass function of our sample by correcting for incompletenesses. Although the
number densities in the massive end are comparable to the theoretical
predictions from semi-analytic models, the number densities in the low-mass
part are smaller than the model predictions. By integrating the stellar mass
function down to 10^8 M_sun, the stellar mass density at z~5 is calculated to
be (0.7-2.4)x10^7M_sun Mpc^-3. The stellar mass density at z~5 is dominated by
massive part of the stellar mass function. Compared with other observational
studies and the model predictions, the mass density of our sample is consistent
with general trend of the increase of the stellar mass density with time.
