A fluctuating oscillator includes: an adder that has an input terminal to which an input signal including a main signal and an uncorrelated signal that is uncorrelated with the main signal and is higher in frequency than the main signal is input, and adds a feedback signal to the input signal; a threshold discrimination unit that generates a pulse signal by comparing an addition signal added by the adder with a threshold; a transient response unit that generates an output signal by transiently responding the generated pulse signal; and a feedback loop that feeds back the output signal to the adder as the feedback signal.