When switching the mode of a power amplifier between a compressed mode and an uncompressed mode, an accurate transmission power control is realized. A transmission power control method includes calculating an intra-mode output power error from a power setting value in a mode before switching as a comparison standard value error (equal to step ST32), setting a power setting value of a mode to switch to, such that an inter-mode output power error is canceled (equal to step ST33), calculating an intra-mode output power error from a power setting value of a mode to switch to (equal to step ST35), calculating a gain linearity value based on a power setting value of a mode to switch to and the intra-mode output power error (equal to step ST36), and resetting the power setting value of the mode to switch to, that cancels the comparison standard value error in the mode before switching and the output power error in the mode to switch to, based on the gain linearity value (equal to steps ST37 and 38).