A base bias circuit operates like a constant voltage source, and a base bias voltage generated thereby varies according to fluctuation of the environment temperature without being influenced by the supply voltage, to hold a collector bias voltage constant. The insect controlling plastic building materials are manufactured by first blending one or more plastic resins with one or more insect controlling chemical agents to form a blended plastic resininsect controlling chemical agent material. In a modification to the method, attenuations of optical attenuators and gain values of optical amplifiers are set.