PURPOSE: To miniaturize a gyrotron device of high operability at a low cost and reduce a running cost by constituting a magnetic field generator in the gyrotron device of a permanent magnet and electromagnets.

CONSTITUTION: A gyrotron 200 comprises an electron gun 1 for emitting electron beams 9, a permanent magnet 20, electromagnets 30, 31, a generator in the axial direction for generating turning motion in an emitted electron, a cavity resonator 6 for generating a cyclotron resonant maser function in a turning electron, a collector 7, and an output window 8 for high frequency 10. A magnetic field exhibits a substantial function for an oscillating operation of the gyrotron 100. The resonator 6 must accurately regulate the magnetic field in accordance with oscillation frequency in an inherent mode. For example, the permanent magnet 20 generates 4kG of magnetic flux density in the axial direction of about 5kG required for obtaining oscillation of frequency 28GHz at a double harmonic oscillation, and the main magnetic field finely adjusting electromagnet 30 generates the remainder 1kG.