With the international trend of the lunar exploration including the ARTTEMIS Plan, we are focusing on the lunar water resource exploration and the neutron lifetime measurement around the Moon by the radiation measurement of neutrons. We are developing a radiation monitor for neutrons and gamma rays, the Moon Moisture Targeting Observatory (MoMoTarO), which is mounted on a lunar rover or a lunar orbiter. The non-contact water exploration without excavation can be realized by measuring the difference in the number of thermal or epi-thermal neutrons depending on water content. The MoMoTarO can also challenge the measurement of the neutron lifetime and the gamma-ray bursts around the Moon. The MoMoTarO is in the process of developing a laboratory model and designing a space-environment model.