In order to boost production of a product of an existing separation plant, an additional plant is integrated with the original plant so as to enable the original plant to produce more of that product, whilst the additional plant may or may not necessarily itself produce the same product directly. Output characteristics of the amplifier circuit are improved and the semiconductor device with high reliability is obtained. , and during operations a change of the peak temperature T of the catalyst in a tube axis direction is maintained in a definite range.