A first transistor is provided in a first route and a second transistor is provided in a second route, the first route and the second route constituting a current mirror circuit. The sources of the transistors are grounded. In order to match VDS of the first transistor and that of the second transistor match each other, there are provided an operational amplifier receiving the drain voltages of the transistors, and a third transistor having a gate thereof connected to the output of the operational amplifier. The third transistor is provided in the first route. As a result, the current fed to the third transistor is controlled so that VDS of the first transistor and that of the second transistor match each other.