A communication semiconductor integrated circuit device is capable of transmission in two or more different modulation modes and outputting transmission signals with less distortion. The communication semiconductor integrated circuit device comprises a gain variable amplification circuit which amplifies I-signals and Q-signals; and a mixer circuit which synthesizes the amplified I-signals and Q-signals and local oscillation signals to carry out modulation and frequency conversion. The communication semiconductor integrated circuit device is capable of transmission in two or more different modulation methods, for example, in GSM mode and EDGE mode. A low-pass filter of second or higher order is placed between the gain variable amplification circuit and the mixer circuit.