Significant advances in microwave and millimeter wave technology have enabled the development of a new generation of imaging diagnostics as a visualization tool in this frequency region. Millimeter-wave imaging diagnostic system is expected to be one of the most promising diagnostic methods that measure profiles and fluctuations of magnetically confined plasmas. It successfully measures the time evolutions of both radial and axial profiles of density and electron temperature and their fluctuation components in a tandem mirror plasma as well as tokamak plasmas. This paper presents the representative results obtained via imaging systems such as phase imaging interferometry, electron cyclotron emission imaging, and microwave imaging reflectometry.