Cold fusion has been investigated by the electrolytical method and the deuterium absorption method. In one of the five runs of the electrolytical experiments a neutron burst was observed at the 90th hour after starting the electrolysis. The detected neutron burst lasted about 4 hours with an intensity of 400 fusions per second. Counting rates of the BF3 long neutron counter and the liquid scintillation detector were simultaneously increased by a factor of 15 compared to the background. A recoil proton energy spectrum of 2.45 MeV neutrons was also measured by the liquid scintillation detector with n-γ discrimination.