A loop heat pipe includes an evaporator, a condenser, and a vapor line and a liquid line each connecting the evaporator with the condenser to form a closed loop. A predetermined quantity of bi-phase working medium is contained in the closed loop. A separator connects the liquid line. A cross section of the separator is larger than a cross section of the liquid line. The separator separates the liquid state working medium from the vapor state working medium when the working medium flows therethrough.