A transmission circuit (4 to 6, 210) for generating a transmission signal based on input data and outputting the transmission signal, the transmission circuit (4 to 6, 210) comprising: a signal generation section for generating a vector signal including I and Q signals and an amplitude signal representing a magnitude of the vector signal, based on the input data; a vector modulation section for performing vector modulation on the vector signal; an amplification section (15a, 15b) for amplifying the signal processed with vector modulation by the vector modulation section; a signal processing section for performing predetermined signal processing on the amplitude signal and outputting the resultant signal; and a regulator for controlling a voltage to be supplied to the amplification section based on a magnitude of the signal which is output from the signal processing section; wherein: the signal processing section: holds at least one threshold value and at least two discrete values corresponding to the threshold value; and determines whether or not the amplitude signal exceeds the threshold value at an interval of a predetermined time period, selects a discrete value to be output based on the determination result, and outputs a signal having the selected discrete value characterized in that 475405-Matsushita-a2-clean copy.docx the signal processing section changes a length of the predetermined time period in accordance with a modulation mode of the transmission signal in order to reduce the power consumption of the transmission circuit (4 to 6, 210). a signal generation section for generating a vector signal including I and Q signals and an amplitude signal representing a magnitude of the vector signal, based on the input data; a vector modulation section for performing vector modulation on the vector signal; an amplification section (15a, 15b) for amplifying the signal processed with vector modulation by the vector modulation section; a signal processing section for performing predetermined signal processing on the amplitude signal and outputting the resultant signal; and a regulator for controlling a voltage to be supplied to the amplification section based on a magnitude of the signal which is output from the signal processing section; the signal processing section: holds at least one threshold value and at least two discrete values corresponding to the threshold value; and determines whether or not the amplitude signal exceeds the threshold value at an interval of a predetermined time period, selects a discrete value to be output based on the determination result, and outputs a signal having the selected discrete value characterized in that 475405-Matsushita-a2-clean copy.docx holds at least one threshold value and at least two discrete values corresponding to the threshold value; and determines whether or not the amplitude signal exceeds the threshold value at an interval of a predetermined time period, selects a discrete value to be output based on the determination result, and outputs a signal having the selected discrete value the signal processing section changes a length of the predetermined time period in accordance with a modulation mode of the transmission signal in order to reduce the power consumption of the transmission circuit (4 to 6, 210).