Toward the confirmation of atmospheric neutrino oscillations

The atmospheric muon neutrino deficit, which was possible evidence of ${\nu }_{\mu }\leftrightarrow {\nu }_{\tau }$ oscillation, was reported by the Kamiokande experiment from 1988. Many experimental efforts were made to examine the Kamiokande results. Experiments which contributed to the confirmation of ${\nu }_{\mu }\leftrightarrow {\nu }_{\tau }$ oscillation are reviewed. Especially, long-baseline neutrino-oscillation experiments are described in detail.