To provide a variable bias circuit which has its high working efficiency with no distortions and can reduce its power consumption.

This variable bias circuit previously stores the value corresponding to the bias current value that is suitable to the working frequency in an MPU 4. Then the bias circuit reads the value out of the MPU 4 in response to the working frequency and applies the D/A conversion to the value via a D/A converter 5 to generate the voltage Vd. Then the bias current that is decided by the voltage Vd and the resistances Rb and R1 is applied to a transistor Q1.