To provide a loop heat pipe capable of preventing both a scattering phenomenon and a water hammer phenomenon and suppressing the deterioration of efficiency in heat transport.

The loop heat pipe encloses a working fluid condensed by heating, evaporation, and radiation, and includes a condenser 7 for condensing a gas phase working fluid, a liquid flow pipe 14 through which a liquid phase working fluid generated by the condenser 7 flows in one direction, an inlet 16 into which the liquid phase working fluid flows in, and an outlet 17 from which a gas phase working fluid flows out where an evaporator 6 for evaporating the liquid phase working liquid flown in from the inlet 16 through the liquid flow pipe 14 and a steam flow pipe 22 connected to the outlet 17 of the evaporator 6 and the condenser 7 so that the gas phase working fluid generated at the evaporator 6 flows to the condenser 7 in one direction are annularly connected. Furthermore, the steam flow pipe 22 or the outlet 17 of the evaporator 6 and the inlet 16 of the evaporator 6 are connected and a liquid bypass pipe 23 is arranged in a way that the liquid phase working fluid generated at the steam flow pipe 22 flows to the inlet 16 of the evaporator 6 in one direction.