A portable electronic device includes a body, a heat source, an evaporator, a pipe, and at least one structural component. An inner space of the body is divided into a first space and a second space. The heat source is disposed at the first space and in thermal contact with the evaporator. The pipe is connected with the evaporator to form a loop and passes through at least one of the first space and the second space. At least a portion of the pipe surrounds and is in thermal contact with the structural component disposed inside the body. A working fluid is filled and is circulated in the loop. By absorbing heat in the evaporator, the working fluid in liquid state is vaporized to exit the evaporator. While passing through the pipe, the working fluid in vapor state dissipates heat to be condensed into liquid and flow into the evaporator.