[en] Neutron guide tubes were innovated at JRR-3 at the same time as JRR-3 was reconstructed, so that much more effective and efficient neutron beam experiments could be carried out. Two tubes were built for thermal neutrons and three for cold neutrons. These guide tubes been used for installing a large number of experimental apparatuses in the wide beam hall and for making a lot of experiments together. The thermal neutron guide tubes were exchanged from Ni-mirror guides to super-mirror ones during the three from 2000. As a result, the thermal beam intensity has increased by about 6 times, and brought more quickness and preciseness into thermal neutron experiments. The Department of Research Reactor and Tandem Accelerator has planned the project of increasing cold neutron intensities by ten times by upgrading both of the cold neutron guide tubes with super-mirrors and the moderator cell of cold neutron source. The front parts of the cold neutron guide tubes are longer than the thermal ones and installed very close to the reactor core. Therefore, we need to work under high levels of radiation when we exchange the cold ones. In addition to that, we have to take away the beam shutter of about 6 ton from the narrow guide tunnel prior to the exchange. In this tight condition, we have to pay attention to installing the tubes as precisely as possible. This report describes the result of study on replacing the Ni-guide tubes with super-mirror guide tubes as the first step of the 10-times upgrading project for cold neutrons. (author)