A transmission circuit is provided which can quickly and accurately control an output power of a transmission signal even when the transmission signal is output at a high modulation rate and in a wide dynamic range. A switching control section controls a modulation method changing section to change a modulation method of a modulated signal generating section to a modulation method having a narrow dynamic range before controlling a switching section to switch amplification sections. An output adjustment control section controls output adjusting sections so that a difference in level between a transmission signal which is smoothed by a smoothing circuit and is before the amplification sections are switched, and a transmission signal which is after the amplification sections are switched, is caused to be smaller than a predetermined difference threshold value, when the modulated signal generating section operates in the modulation method having the narrow dynamic range.