There is provided a power source circuit (100) which supplies power from a first power source (1) when the first power source that stops feeding upon consumption of a current of a predetermined value or more, and a second power source (9) lower in voltage than the first power source are connected simultaneously. The power source circuit includes a switching unit (5) which controls power supply from a control unit (2) for controlling feeding from the first power source, a charge accumulation unit (3) which accumulates charges between the control unit and the switching unit, and a charging detection unit (4) which outputs, to the switching unit, a signal for performing the power supply when it is detected that the difference between a voltage charged in the charge accumulation unit and a feed voltage from the control unit is equal to or smaller than a designated value.