Relatively large electro-optic effects of nematic liquid crystal (LC) in the millimeter wavelength region have the possibility of an application to the electrically controlled millimeter-wave devices. The millimeter-wave transmission properties of the conventional nematic LC cells with a grating-patterned electrode structure are described. Novel LC cells with a stack-layered structure using metal substrates, which have a large effective path length, are prepared and large millimeter-wave transmission modulation of 50% can be attained by applying an external electric field to the LC cell. The stack-layered structure is useful for an application to the millimeter-wave devices. Then, the LC prism and LC lens as the quasi-optical millimeter-wave devices using the stack-layered structure are proposed. Deflection and focusing effects of the millimeter-wave are observed by applying an external electric field to the LC cells.