A Lepton Flavour Violation (LFV) among charged leptons, e.g. $\mu \rightarrow e \gamma$ (mu-e-gamma), $\mu N \rightarrow e N$ (mu-e conversion) etc, which has never been observed while the quark mixing and the neutrino oscillations have been experimentally confirmed, is attracting a great deal of attention, since its observation is highly expected by most of well-motivated theories beyond the Standard Model, such as SUSY-GUT, seesaw, little-Higgs, etc.
Since the high power muon source is available at PSI and J-PARC recently, precise measurement of muon decay is most promising to search for the charged LFV.
In this presentation, the latest and final result of MEG experiment which is the present upper limit will be given in detail.
In addition, some experimental prospects will be presented to search for several muon LFV process such as MEG-II to explore mu-e-gamma one order more, and COMET/mu2e to search for mu-e conversion four orders more, and so on.