A fuel cell 1 and an electric double-layer capacitor 2 are parallelly arranged for a power supply. A DC/DC converter 3 steps up voltage of the fuel cell 1 and the electric double-layer capacitor 2, to thereby output power. An output switch 5 is disposed on an output pathway of the DC/DC converter 3. By controlling the output switch 5 with a control IC 4, output power can be switched on and off. When there is a fuel shortage or abnormality in the fuel cell 1, the control IC 4 controls the output switch 5, to thereby intermittently alter the output power. With this configuration, when the power supply is used for a mobile telephone as a portable electronic device connected thereto, a user can confirm whether there is a fuel shortage or a fuel cell abnormality by checking of blinking state of a charge pilot lamp of the mobile telephone.