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.