We propose to perform neutron diffraction experiments on a powder sample of the frustrated triangular lattice antiferromagnets α-NaFeO2 under high-pressure up to 18 kbar using WISH. In previous studies of α-NaFeO2, the magnetic structures of the ground state (T < 5 K) and intermediate temperature phase (5 K < T < 10.5 K) have been investigated.[1] This magnetic ground state is a commensurate structure with k=(1/4, -1/4, 1), which is a very rare state for the ground state of triangular lattice magnets (it would become 120 degree structure in ideal Heisenberg triangular lattice model). Quite recently, we have found significant effect of hydrostatic pressure on the magnetic susceptibility of α-NaFeO2. In this work, we want to investigate the high-pressure effect on the magnetic structures of α-NaFeO2 through neutron diffraction under pressure on WISH.