PURPOSE: To increase a voltage range that contribute to an amplifying action, to attain the effective use of the power voltage, and to acquire a useful technique for the use of the power voltage of a low level by setting the value of a resistance element at a level larger than a prescribed level and also smaller than infinity.

CONSTITUTION: A line A' shows a load line defined when the value of a resistance element R is calculated from an equation, i.e., the line A' is equivalent to a conventional load line defined when the value of the element R is set at RLJ. A line B shows a load line that has a slant smaller than the load line A'. The value RL of the element R can be set larger (limited less than infinity) than the value RLJ for the load line B. In the equation, VDS shows the drain- source voltage (or collector-emitter voltage) of a transistor TR and ID shows the largest saturated current that can be supplied by the TR. As a result, a voltage range that contribute to an amplifying action is increased and the power voltage is effectively used. Then a useful technique is acquired for the use of the power voltage of a low level in particular.