An atomic oscillator includes an atomic cell in which an atom is enclosed, a magnetic field generation part to apply a magnetic field to the atomic cell, a reference oscillator which is controlled based on an atomic resonance signal outputted from the atomic cell and generates a reference signal, and a fractional N-PLL which receives the reference signal to generate a signal including a resonance frequency of the atom, in which when a maximum digit of the resonance frequency adjustable by the magnetic field generation part is a boundary digit, the fractional N-PLL can adjust at least a digit one digit higher than the boundary digit.