The present invention provides an atomic oscillator comprising: a first frequency synthesizer for multiplying a reference frequency signal oscillated with a first voltage control oscillator by a first multiplication ratio and synthesizing a first high frequency signal; a first semiconductor laser for emitting a first laser light modulated by the first high frequency signal; a second frequency synthesizer for multiplying an output signal oscillated by a second voltage control oscillator with a second multiplication ratio and synthesizing a second high frequency signal; a second semiconductor laser for emitting a second laser modulated by the second high frequency signal; a gas cell being emitted with the first laser light and the second laser light simultaneously, the gas cell enclosing a first alkali-metal atom gas, a second alkali-metal atom gas, and buffer gas; and a computer for setting the first multiplication ratio in the first frequency synthesizer.