An objective of this invention is to obtain a signal processing circuit and a signal processing method that reduce temperature-induced distortion when inputting a signal to a mixer and changing the frequency of the signal to a desired frequency. If a sensing result from a temperature sensor 133 is lower than a predetermined temperature, the attenuation factor of a first variable attenuator 102 is large while the attenuation factor of a second variable attenuator 108 is small. The magnitude relationship between the attenuation factors is reversed in a temperature range of the predetermined temperature or more. In a mixer 104 in which at a low temperature, the gain increases, and distortion increases, an increase in IM3 distortion can be prevented by increasing the attenuation factor at a low temperature. The same applies to a case where a mixer that has an amplifier arranged at a preceding stage thereof and makes the amplification factor of the amplifier large at a low temperature is used. An amplification factor may be adjusted instead of an attenuation factor.