An extremely low-lying nuclear isomer in Th-229 is still to be established in spite of efforts made since the first postulation of the isomer in 1976. To study such an extremely low-lying nuclear isomer, we have built an entirely new device that is based on the well-established atomic spectroscopic technique: Hollow-cathode discharge, The isomer in question is expected to be populated by the process NEET through atomic excited states if it exists in an energy range of electron volt. After switching off the discharge, we will measure alphas from the isomer, photons from the isomer itself and photons from atomic states to which the isomer is expected to decay by the inverse NEET. Our experiment is under way at Oarai using the world's radiochemically purest Th-229 sample.