A working medium property difference power generation system that uses thermal energy existing in a natural world, as a thermal source of a working medium, the working medium property difference power generation system comprising configurations A to D described below: A: a first working medium line that circulates a first working medium, and a second working medium line that circulates a second working medium are included; B: a first heat exchanger for performing thermal exchange between the first working medium and a thermal source medium (h), a first thermal engine configured to take out kinetic energy from the first working medium heated by the first heat exchanger, and a first power generator configured to convert the kinetic energy taken out by the first thermal engine, into electrical energy are included on the first working medium line; C: a second heat exchanger for performing thermal exchange between the second working medium and a thermal source medium (h), a third working medium supply mean; configured to supply a third working medium to be mixed with the second working medium heated by the second heat exchanger, a mixing means configured to mix the second working medium and the third working medium, a second thermal engine configured to take out kinetic energy from mixed fluid of the second working medium and the third working medium, and a second power generator configured to convert the kinetic energy taken out by the second thermal engine, into electrical energy are included on the second working medium line; and D: on both of a downstream side of the first thermal engine of the first working medium line and a downstream side of the second thermal engine on the second working medium line, a third heat exchanger for performing thermal exchange between the first working medium discharged from the first thermal engine, and mixed fluid of the second working medium and the third working medium that is discharged from the second thermal engine is included, and a third working medium discharge means for discharging the third working medium from the third heat exchanger is included. A: a first working medium line that circulates a first working medium, and a second working medium line that circulates a second working medium are included; B: a first heat exchanger for performing thermal exchange between the first working medium and a thermal source medium (h), a first thermal engine configured to take out kinetic energy from the first working medium heated by the first heat exchanger, and a first power generator configured to convert the kinetic energy taken out by the first thermal engine, into electrical energy are included on the first working medium line; C: a second heat exchanger for performing thermal exchange between the second working medium and a thermal source medium (h), a third working medium supply mean; configured to supply a third working medium to be mixed with the second working medium heated by the second heat exchanger, a mixing means configured to mix the second working medium and the third working medium, a second thermal engine configured to take out kinetic energy from mixed fluid of the second working medium and the third working medium, and a second power generator configured to convert the kinetic energy taken out by the second thermal engine, into electrical energy are included on the second working medium line; and D: on both of a downstream side of the first thermal engine of the first working medium line and a downstream side of the second thermal engine on the second working medium line, a third heat exchanger for performing thermal exchange between the first working medium discharged from the first thermal engine, and mixed fluid of the second working medium and the third working medium that is discharged from the second thermal engine is included, and a third working medium discharge means for discharging the third working medium from the third heat exchanger is included.