PURPOSE: To minimize the CN ratio by amplifying the power after attenuating both the radio frequency signal and the noise component through an attenuator when the transmission power is reduced, amplifying the power of the radio frequency signal without passing through the attenuator contrary when the transmission power is increased, and making the output level of a variable gain amplifier constant in any case.

CONSTITUTION: A transmission power control circuit 7 decides the prescribed power value to be controlled within the allowable variable range of the transmission power and the upper and lower respective ranges are handled as the control range of the transmission power. When the transmission power becomes higher than the prescribed power value, in order to make the former small a radio frequency signal to be outputted from a mixer 3 is attenuated through an attenuator 8 and outputted to a final output stage 5. In this case, the noise component included in the radio frequency signal is attenuated at the same time. The output level of a 2nd local oscillation signal LO2 to be outputted from a variable gain amplifier 4 is kept the constant level by a gain adjustment signal.