A power supply circuit uses a rechargeable battery that if a connection switching unit changes to a circuit connected state, a current starts to be supplied from the rechargeable battery to an over-discharge protection circuit, a logic circuit, and a power supply control circuit, and if the connection switching unit changes to a circuit non-connected state during this current supply, the current supplied to the over-discharge protection circuit, the logic circuit, and the power supply control circuit is maintained, and a current supplied from the rechargeable battery to the load circuit is started by supplying the current from the power supply control circuit to the load circuit, and if a voltage of the rechargeable battery drops while the current is supplied to the load circuit, and the over-discharge protection circuit stops the current supplied from the rechargeable battery to the load circuit, the over-discharge protection circuit maintains the stopped state.