  A collider probe of the radiative seesaw models are considered. Two key
ingredients of these models, the extended Higgs sector and the source of the
Majorana mass, although these details differ model by model, would be studied
at the TeV-scale electron-positron and electron-electron colliders. The
searches and mass determinations in the inert doublet model, which is the
extended Higgs sector of the Ma model, are summarized as an example.
