A digital camera has a battery that supplies electric power, a battery level detector, a time detector, a remaining voltage calculator, and a boot controller. When the digital camera is turned off, the battery level detector detects a remaining voltage level of the battery. When the digital camera is turned on, the time detector detects an elapsed time from the last electric power OFF operation to the current electric power ON operation, namely, a time period in which the camera is in the OFF state. Further, when the digital camera is turned on, the remaining voltage calculator calculates a remaining voltage-level of the battery on the basis of the detected elapsed time, the last detected remaining voltage level, and the discharge characteristic of the battery. Then, the boot controller allows the digital camera to boot if the calculated remaining voltage level is larger than a limited voltage necessary to boot the digital camera.