We propose to perform neutron diffraction experiment under high pressure condition, using a single crystal of CuO on WISH beamline. This monoxide is known as a multiferroic compound with high Tc (~ 230 K). Some theoretical and experimental studies suggest that pressure significantly affects the phase transition, bringing Tc above room temperature. However, there remains inconsistencies among the different theoretical studies and the experimental results. In this work, we would like to investigate how the ferroelectric phase transition temperature changes with pressure by using a single crystal of CuO in the experimentally accessible pressure range up to 10 GPa.