A 1 MW, cw, Free Electron Maser is being designed for ECRH applications on ITER . The FEM will be tunable over 10% of the central frequency of 200 GHz. Furthermore, experiments at 250 GHz and -later on- 130 GHz are foreseen. The FEM uses a thermionic electron gun and a 2 MeV electrostatic accelerator . The required fast tunability is achieved by variation of the accelerator voltage. The undulator and mmw system are located inside a terminal at a voltage of 2 MV. The terminal is placed inside a steel vessel of 10 m long and q 2.5 m, filled with SF6 at 6 bar. The layout is shown in Fig. 1. After interaction with the mm waves in the undulator, the energy of the electron beam will be recovered by means of a decelerator and a multi-stage depressed collector. This will bring the overall efficiency to a very high level. The voltage for an FEM is much higher than for other high-power mm-wave sources, like gyrotrons and CARMs. However, the main current has to be supplied at a voltage of not more than a few hundred kV. The 2 MV power supply has to deliver the electron-beam current lost during transport, therefore the loss of electrons has to be limited to approximately 20 mA. For this reason and also to enable an efficient energy recovery, a simple straight electron-beam line will be used.