A gas cell unit has a gas cell, inside which a gaseous alkali metal atom is sealed, a heater that heats the gas cell. The heater includes a heating resistor including a plurality of band-like portions so as to be parallel to each other. By making the directions of electric current flowing through two band-like portions adjacent to each other opposite to each other, it is possible to mutually offset or alleviate the magnetic fields generated along with the electric conduction to the plurality of band-like portions.