In the digital camera that can be used in connection to a mobile phone or other mobile electronic devices and the system thereof, a battery mounted in each device is shared to allow power to be supplied between the devices, and allow both devices to be used for longer hours. The digital camera and the mobile phone are electrically connectable by a connection cable. Generally, a power supply selection switch is set to A, and a power supply selection switch is set to D. The digital camera receives power supplied from a battery, and the mobile phone receives power supplied form a battery. From this state, when the power supply selection switch is switched to C, power is supplied from the battery to the mobile phone. On the other hand, when the power supply selection switch is set to B, and the power supply selection switch is set to D, power is supplied from the battery of the mobile phone to the digital camera.