PURPOSE: To prevent a recording sheet which obstructs the flow of developer at a slit-like aperture part for developing from being curved, to always perform the development of high quality without being influenced by the difference of the kind of the recording sheet even when a large-sized and complicated carrying mechanism is not used, and further to perform excellent development without unevenness over the entire width though a developing head is simple and its production is easy.

CONSTITUTION: The aperture 3a capable of introducing the developer from the outside and the aperture 3b capable of discharging the developer to the outside are formed in parallel on the upper surface of a base substance. Division grooves 25a and 25b nearly in parallel with the apertures 3a and 3b are formed between the apertures 3a and 3b. Then, many groove parts 26a, 26b and 26c which obliquely link two paths and are parallel with each other are formed between two adjacent paths out of the respective paths.