PURPOSE: To provide a magnetohydrodynamic generation (MHD generation) method and apparatus therefor which method can retain a high enthalpy sampling rate while maintaining the flow velocity of a working fluid in an MHD channel at a certain condition, when the flow rate of the working fluid is changed with a load change in magnetohydrodynamic generation.

CONSTITUTION: The optimum mode of power generation is set and the optimum power generation is conducted when the distance (width of flow path) between sidewalls 10a, 10b facing each other and forming the flow path 9 of a working fluid is made variable according to conditions of power generation determined by the flow rate, temperature, etc., of the working fluid to be supplied to a generator. The width (d) of the flow path is optimally adjusted by a working fluid-measuring system 16 provided at the inlet of the generator and by a driver 17 operating while interlocking with the measuring system.