[en] The preliminary experiment of the detection of ultra cold neutrons has been performed. The ultra cold neutrons have the energy of 10^-7 eV. which is smaller than the effective potential from nuclei. Accordingly, the ultra cold neutrons are reflected from the surface of a material. It is possible to confine the ultra cold neutrons in a box with reflective inner surfaces. Neutron bottle experiment was performed by using an electron linear accelerator at Kyoto University Research Reactor Institute. The counting more than background was observed. The measurement of neutron energy by the TOF method was carried out, and it can be said that the ultra cold neutrons were detected. (Kato, T.)