The invention provides a power generating device which comprises a steam boiler, a steam water sprayer, a steam water spraying controller, a back pressure device, a circulating water tank, a hydraulic turbine and a generator. The working process of the power generating device is that: under the control of the steam water spraying controller, high temperature and high pressure steam generated by the steam boiler enter the steam water sprayer to expand for applying work. After water from the circulating water tank to the steam water sprayer is pressurized, high pressure water is output from the outlet of the steam water sprayer; the high pressure water runs through the back pressure device and enters the water guiding mechanism of the hydraulic turbine. When running through a rotating wheel, water current transfers energy with the rotating wheel so as to drive the main shaft of the hydraulic turbine to rotate; the hydraulic turbine drives the generator to externally generate power. The power generating device of the invention realizes the conversion from heat energy to electric energy by utilizing two levels of media which are steam and water, and has the advantages of both a steam power generating device and a water power generating device. The power generating device has a simple and reliable energy conversion mechanism, simple production, low cost, small investment of assorted engineering facilities.