A gain control circuit has a transmission power amplifier that amplifies a transmission signal to a predetermined level. An adjacent channel leak power ratio monitor finds a ratio of a distortion element corresponding to an adjacent channel leak power to a main element from an output signal supplied from the transmission power amplifier, and outputs the found ratio as an ACPR monitor value. A power supply control section variously controls power supply to the transmission power amplifier with use of the ACPR monitor value supplied from the adjacent channel leak power ratio monitor. A transmission signal level variable section controls a gain of a transmission signal path on the basis of a transmission level monitor value supplied from the adjacent channel leak power ratio monitor, thereby varying a level of the transmission signal.