Layered oxypnictide LaOMnAs shows an antiferromagnetic insulator-to-ferromagnetic metal transition at room temperature with increasing the defect of LaO layer which induces hole doping into the MnAs layers. In order to reveal the details of the transition, we have performed hard-X-ray photoelectron spectroscopy for the insulating LaOMnAs and metallic (LaO)0.7MnAs. The spectral changes in the valence band, mainly composed of Mn 3d states, Mn 2p core levels, and La 3d core-levels have been observed across the transition. Our results indicated that Mn 3d state was significantly influenced by the defect of LaO layer.