It is an object of the present invention to realize a SIR detection device and a radio communication device capable of detecting the value of a ratio of a signal component to an interference component (SIR: Signal to Interference Ratio) indicating the power ratio of a signal component to an interference component of a radio signal with precision. To attain this object, the SIR is detected, a value of power N added to the radio signal by internal noise of a radio processing section (4) is determined based on a NF (Noise Figure) of the radio processing section that performs analog signal processing in a RF (Radio Frequency) area of the radio signal, a value of power I of an interference component included in the radio signal is determined based on a RSSI (Received Signal Strength Indicator) indicating reception strength of the radio signal, and calculation is performed on the detected SIR value with the amount of correction based on the power N of the internal noise and the power I of the interference component, thereby making a correction of removing the power N of the internal noise included in the SIR.