A semiconductor device includes a first electrical current source connected to an assembled battery through a power source terminal; and a second electrical current source connected to an input terminal to which an external electrical current is input. The first electrical current source is configured to generate a first electrical current according to a reference voltage based on a power source electrical current input into the power source terminal, and to output the first electrical current to an output terminal. The second electrical current source is configured to generate a second electrical current according to the reference voltage based on the external electrical current, and to output the second electrical current to the output terminal.