A retort sterilization device includes a water steam generation device for generating water steam and a heating pot, connected to the water steam generation device, for accommodating retort food. The water steam generation device includes a heat exchanger for performing heat exchange between liquid flowing in a liquid path and heating vapor flowing in the vapor path. A top end of the liquid path of the heat exchanger is connected via a water steam supply pipe to a water steam ejection section located in an internal area of the heating pot. The heat exchanger is connected to a liquid container. A bottom end of the liquid path of the heat exchanger is connected to the liquid container via a communicating tube. The liquid container is coupled to the heating pot.