PURPOSE: To obtain a power supply for an electronic apparatus which can be operated continuously without paying attention to consumption thereof.

CONSTITUTION: An electronic apparatus 1 is loaded with a plurality of secondary power supplies Ba, Bb and provided with a mechanism for selecting a secondary power supply having highest voltage thus operating the electronic apparatus 1 continuously. The electronic apparatus 1 is also provided with a mechanism for preventing a currently working power supply from being removed inadvertently to cause missing of generated data. With such constitution, the electronic apparatus can be operated continuously without paying attention to consumption of the power supply. Furthermore, generated data is protected against missing because a working power supply in the electronic apparatus is prevented from being removed inadvertently.