A constant temperature liquid bath using a thermo-module in which even if an article whose temperature is to be controlled exists in the bath, the temperature of the liquid is efficiently adjusted to a constant value. The liquid bath includes an outer bath storing the liquid, an inner bath disposed in the outer bath through a gap, and including holes in its sidewall through which the liquid flows into the inner bath from the outer bath and an opening at a central portion of its bottom, and an agitator that causes the liquid to flow upward from the opening of the bottom of the inner bath between sidewalls of the inner and outer baths by a rotor blade disposed on a central portion of a bottom between the outer bath and the inner bath. The thermo-module is mounted on an outer surface of the sidewall of the outer bath.