TECHNOLOGY FOCUS - ELECTRONICS - Preferred Components: A sensor (51, 32, 34) detects day and time, a position of the system or an illumination surrounding the system. The controller further functions to estimate the shift of outside air temperature based on the detected day and time, detected system position or detected illumination. The controller may further function to estimate the shift of outside air temperature based on an input climactic information. A sensor (33) detects outside air temperature and the controller further functions to correct the estimated outside air temperature shift based on the difference between the outside air temperature obtained from the estimated outside air temperature shift and the detected outside air temperature. The controller further functions to apply a difference between an actual restart time when the fuel cell actually restarts and the estimated restart time to the estimation of restart time on the next occasion. When there is an input restart time, the controller further functions to estimate that the fuel cell restarts at the input restart time. The controller further functions to correct the estimated restart time when the fuel cell is not restarted although a predetermined time after the estimated restart time has elapsed and perform the protection mode selection again based on the corrected restart time. It may function to correct the estimated restart time based on a difference between the estimated restart time and an actual restart time. A sensor (31, 36, 35) detects a remaining energy amount in the system or an oxygen concentration outside the system and the controller further functions to stop protection in the first protection mode when the detected remaining energy amount or a detected oxygen concentration outside the system is lower than a predetermined value. An alarm device (41, 42) issues an alarm when the remaining energy amount in the system is less than a predetermined value. The controller further functions to start thawing ice which has frozen outside the fuel cell from a predetermined time prior to the estimated restart time when the system is protected in the second protection mode. A switch (53) starts the fuel cell. The controller further functions to stop protecting the system and start the fuel cell when the switch is operated when the system is protected by the first or second protection mode.