PURPOSE: To enable power generation at a low temperature by a method wherein ionization raw material being liable to be ionized is used as a working fluid.

CONSTITUTION: A working fluid 9a in liquid as ionization raw material being liable to be ionized is vaporized by a heat source 10 in a primary cooling section 6, and becomes a working fluid 9b in vapor at high temperature and high pressure. On the other hand, in a secondary cooling section 7, the working fluid 9b in vapor is cooled by an evaporation pipe 11 and becomes the working fluid 9a in liquld. Since large pressure difference is produced between both cooling sections 6, 7, the working fluid 9b in vapor flows at high speed in a flow path 2 of an MHD generator 1 and magnetic field is given to the fluid by an electromagnet 4, and power is taken from an electrode 3.