  We report on magnetic characteristics in four-layered high-T_c
superconductors Ba_2Ca_3Cu_4O_8(F_yO_{1-y})_2 with apical fluorine through Cu-
and F-NMR measurements. The substitution of oxygen for fluorine at the apical
site increases the carrier density (N_h) and T_c from 55 K up to 102 K. The NMR
measurements reveal that antiferromagnetic order, which can uniformly coexist
with superconductivity, exists up to N_h = 0.15, which is somewhat smaller than
N_h = 0.17 being the quantum critical point (QCP) for five-layered compounds.
The fact that the QCP for the four-layered compounds moves to a region of lower
carrier density than for five-layered ones ensures that the decrease in the
number of CuO_2 layers makes an interlayer magnetic coupling weaker.
