A handheld electronic device includes a case, an electronic unit and a cooling fan. The case includes at least one rib, an air inlet and a heat outlet. The at least one rib delimits a heat chamber. The air inlet and the heat outlet intercommunicate with an outside of the case. The electronic unit includes a heat source located in the heat chamber. The cooling fan is located in the heat chamber and includes an air entrance and an air exit. The air entrance intercommunicates with the air inlet of the case, and the air exit intercommunicates with the heat outlet of the case.