An automotive turbocharger uses exhaust gas to rotate the turbine, and then the compressor bladed wheel, the shaft of which is connected directly with the shaft of the turbine, is driven. A standard turbocharger uses a single scroll turbine. However, at lower engine speed, it cannot compress air supply sufficiently because exhaust gas flow is small and the boost pressure is low. To raise boost pressure, a twin scroll turbine is effective(1).