PURPOSE: To prevent generation in a power supply system of transient current by directly connecting an external power supply to a first power supply line, connecting a large capacitance capacitor to a second power supply line and connecting the first and second power supply lines through a resistor or a transistor.

CONSTITUTION: There are a first power supply line 1, an internal circuit 11 connected to the power supply line, a second power supply line 2 and an internal circuit 12 connected to the second power supply line in a semiconductor integrated circuit 10. An external power supply 20 is connected to the first power supply line 1, and a large capacitance capacitor 40 is connected to the second power supply line 2. The first power supply line 1 and the second power supply line 2 are connected through a resistor 30. When large charge currents flow in the internal circuit 12, most of the currents are supplied with charge from the capacitor 40, and an effect on the power supply line 1 that is, an effect on the external power supply 20 is eliminated. The titled circuit is effective especially when large currents in the internal circuit 12 do not belong to DC and belong to dynamic charge currents.