  The coexistence of magnetism and superconductivity in the
isovalent-P-substituted BaFe$_2$(As$_{1-x}$P$_x$)$_2$ has been investigated
microscopically by $^{31}$P-NMR measurements. We found that superconducting
(SC) transition occurs in a magnetic region with static ordered moments and
that the moments are reduced below the SC transition temperature $T_{\rm c}$ in
the samples near the phase boundary of magnetism and superconductivity. Our
results indicate that magnetism and superconductivity coexist spatially but
compete with each other on the same Fermi surfaces. The coexistence state is
qualitatively different from that observed in other unconventional
superconductors and gives a strict constraint on the theoretical model for
superconductivity in BaFe$_2$(As$_{1-x}$P$_x$)$_2$.
