A photosensitive material processing apparatus having a processing tank in which a processing solution for processing a photosensitive material is stored, and rollers or the like for conveying the photosensitive material along a predetermined path within the processing tank. By maintaining a humidity of upper portion spaces of the processing tank at greater than or equal to 80%RH, dirtying of machinery due to crystal deposition of processing chemicals and non-uniformity of the processing solution are prevented. In order to maintain the humidity of the upper portion spaces of the processing tank at greater than or equal to 80%RH, a cover having an opening ratio of less than or equal to 40% is disposed at an upper portion of the processing tank, and spaces enclosed by the cover are not ventilated by fans. Further, it is preferable that a ratio of a volume of the upper portion spaces of the processing tank enclosed by a cover to an area of an exposed surface of the solution within the processing tank is 0.5 cm.sup.3 /cm.sup.2 to 10 cm.sup.3 /cm.sup.2.