Physics opportunities of a very intense low-momentum muon source

The front-end of a neutrino factory (or a μ+μ− collider) has a potential to provide a high-intensity muon beam of low energy. It would give us great physics opportunities with a tremendous number of muons (of about 1012/s). Among many possibilities, one of the important physics subjects is a search for muon lepton flavor violation (LFV). The physics motivation of muon LFV and the latest experimental status are given. Finally, a high-intensity muon source, in particular PRISM in Japan, is discussed.