A thermal electric power generator includes an evaporator, an expander, an electric generator, a condenser, and a pump. A working fluid used in the thermal electric power generator is an organic working fluid. The evaporator includes a heat exchanger, a bypass channel, and a flow rate adjustment mechanism. The bypass channel allows a heat medium to bypass the heat exchanger. The flow rate adjustment mechanism adjusts a flow rate of the heat medium to be supplied to the heat exchanger and a flow rate of the heat medium to be supplied to the bypass channel.