A series regulator circuit for supplying voltage with low current consumption without depending on the capacitance of a load. A constant current source, which is connected to an input voltage line, is connected to a ground voltage line via a bipolar transistor. The gate terminals of first and second n-channel MOS transistors are connected between the constant current source and the collector terminal of the bipolar transistor. The drain terminals of the first and second transistors are connected to the input voltage line. The source terminal of the transistor functioning as an output terminal is connected via a first resistor element to the source terminal of the first terminal, which is connected to a ground voltage line via second and third resistor elements. A connection node between the second and third resistor elements is connected to a base voltage of the bipolar transistor.