A count control signal generating section for generating a count control signal on the basis of an output signal of a variable gain amplifier; an up/down counter for performing an up-count operation or a down-count operation on the basis of the count control signal; a gain control signal generating section for generating a gain control signal to be supplied to the variable gain amplifier on the basis of a count value of the up/down counter; and a state detector section for outputting a state detection signal indicating whether a state of a circuit operation is a steady state or another state are provided. When the state detection signal indicates that the state of the circuit operation is the steady state, the operation of at least one of the up/down counter and the gain control signal generating section is controlled so as to fix the gain control signal.