To provide an atomic oscillator that stably exerts desired characteristics by maintaining a gas cell and a light emission section in a predetermined temperature range irrespective of environmental temperature.

An atomic oscillator 1 includes: a first package 6 housing a gas cell 2, a first variable temperature section 41 for controlling the temperature of the gas cell 2, a light emission section 5, and a second variable temperature section 42 for controlling the temperature of the light emission section 5; a third variable temperature section 43 for controlling the temperature of the first package 6; and a control section 8 for controlling the drive of the temperature control sections 41-43. When TL and TH denote lower and upper limit values of environmental temperature where the first variable temperature section 41 can control the gas cell 2 to a predetermined temperature Ta and the second variable temperature section 42 can control the light emission section 5 to a predetermined temperature Tb, the control section 8 is configured to maintain the temperature of the first package 6 at TL or higher and TH or lower by driving the third variable temperature section 43 when the environmental temperature is lower than TL or higher than TH.