First, second and third current generators, and first and second switching devices are provided. Current values of the first and second current generators are equal to each other and a current value of the third current generator is twice as large as the current value of the first and second current generators. The first current generator and the third current generator are connected to each other through the first switching device, and the second current generator and the third current generator are connected to each other through the second switching device. A first output is taken out from a node between the first switching device and the first current generator, and a second output is taken out from a node between the second switching device and the second current generator.