A room temperature heat engine, wherein only one pipe structure for connecting a high pressure part to a low pressure part, which is a fatal structural defect of the room temperature heat engine for decorative toys (water drinking bird, peace bird) which merely produces a weak and small mechanical energy, is improved so as to produce much powerful mechanical energy for practical use of the engine, no energy source being required because the energy used for power generation is a beat obtained from the atmospheric temperature, the high and low temperature parts are connected to each other through at least two pipes, the high temperature and low temperature parts are formed in a stationary large-sized structure, two pipes are used exclusively for a gas-only pipe and a liquid-only pipe, and a turbine wheel is installed in the fluid-only pipe so as to turn the waterwheel under a fluid flow from the low temperature part for power generation.