Abstract: To achieve an object to provide a detachable temporary power source for cellular phone permitting a call for a very long period of time even for a cellular phone requiring a high power consumption, the present invention provides a temporary power source for cellular phone which makes it possible to make a call for a long period of time several times as long as that of a usual built-in power source, and can charge even built-in batteries of the cellular phone. The detachable temporary power source for cellular phone of the invention has a power source such as alkali dry battery, a diode, a regulator and a connector. Voltage supplied from the power source causes the regulator to supply a constant voltage, and has a power supply circuit preventing reverse flow of current from the built-in batteries of the cellular phone under the effect of the diode.