PURPOSE: To correctly detect the battery's capacity even in the case a load of the battery alters and prevent erroneous detection of the decrease of the battery's capacity and an alarming output, regarding an appliance which uses a battery as an electric power source.

CONSTITUTION: Regarding a communication apparatus which uses a battery 8 as an electric power source; in the case a controlling part 7 increases the signal sending outputs in a signal sending part 6 corresponding to the decrease of the intensity of an electric field, the controlling part 7 subsequently compares the voltage of the battery and lowers the standard voltage from a standard voltage power source to detect the decrease of the capacity of the battery. As a result, even if the voltage of the battery lowers to increase the signal sending outputs, following that the standard voltage is lowered, so that the decrease of capacity of the battery due to the decrease of the battery is not detected.