An oscillator includes a first container that includes a first base substrate and a first lid and that has a first internal space, a second container that is fixed to the first base substrate in the first internal space and that includes a second base substrate and a second lid and that has a second internal space, a resonator element that is disposed on the lower surface side of the second base substrate in the second internal space, a temperature sensor that is disposed on the upper surface side of the second base substrate, a first circuit element that includes an oscillation circuit and a second circuit element that is fixed to the first base substrate in the first internal space and that includes a frequency control circuit that controls a frequency of the oscillation signal output by the oscillation circuit. The second container and the second circuit element are arranged side by side in plan view.