Abstract: A quantum effect device which operates in a mesoscopic region and eliminates the need for making monochromatic electron waves for the operation and moreover can operate in a high temperature region. The quantum effect device comprises a first waveguide for connecting a first region and a second region, wherein carriers are injected into the first region and emitted from the second region, a second waveguide being branched off from the center of the first waveguide and connected to a third region, and a control region being formed in the branch part of the first and second waveguides for controlling a potential barrier. When the potential barrier is low, the control region emits carriers on the first waveguide from the second region and when the potential barrier is high, the control region leads carriers into the second waveguide from the first waveguide by quantum-mechanical reflection for emitting the carriers from the third region.