Even if a receiver has a normal gain and a lowered intermodulation distortion characteristics, a fault detection is possible. A test signal transmitter sends a test signal having at least two frequencies to a radio receiver through a coupler. A digital signal processing section receives a signal which includes an IM3 component generated by the radio receiver and measures the electric power of fundamental wave components and the IM3 component. Then, the digital signal processing section calculates the gain of the radio receiver and IIP3, which is an index for intermodulation distortion characteristics, of the radio receiver 207 from the calculated electric power. A base station control section determines whether the gain and IIP3 of the radio receiver fall in predetermined ranges to determine whether the radio receiver works normally or has a fault.