To provide a developing unit capable of suppressing a temperature rise of the exterior surface of the unit by heat emitted from a drying section and capable of shortening the waiting time until the drying section attains a set temperature and to provide an image recording apparatus.

The developing unit includes a processing tank for developing photosensitive paper exposed according to image information while conveying the paper and a drying section in a unit case, and a space 41 comparted between the drying section 26 and an exterior part 21b of the unit case 21a is provided near the drying section, and an open-air passage 42 is provided between the drying section and the exterior part of the unit case so that the open air is introduced into the drying section or a part near the section.