An immersion type automatic developing apparatus for a lithographic printing plate in which removal of a non-image area is conducted in a state where a lithographic printing plate precursor having on a support an image-recording layer exposed imagewise is immersed in a developing bath filled with an aqueous solution containing a carbonate ion, a hydrogen carbonate ion and a water-soluble polymer compound, wherein a developer composed of the aqueous solution is circulated between the immersion type developing bath forming a processing pass line and an external tank provided outside the processing path line so as to keep constant a liquid level of the immersion type developing bath.