Four stochastic resonators 20-1 to 20-4 outputting a pulse signal in accordance with a stochastic resonance phenomenon are unidirectionally coupled in a ring-like form to constitute a fluctuation oscillator 10. When a signal output from each of the stochastic resonators 20-1 to 20-4 is successively transmitted in the stochastic resonators 20-1 to 20-4 coupled in a ring-like form, the output timings at each stochastic resonator 20 are synchronized with each other due to a cooperation phenomenon between the stochastic resonators 20-1 to 20-4, so that each stochastic resonator 20 is self-excited to oscillate at a constant period of time.