PURPOSE: To simplify an auxiliary facility related to development and to make a developing head small in size, light in weight and low at cost by constituting a magnet so that it allows the peripheral surface of a roller to rub and rotate on a regulating surface.

CONSTITUTION: Developer passes a developer supply port 27 and is introduced in a box unit 30 and discharged from a drainage port 28. The liquid level of the developer is positioned by a regulating end 29. The developing roller 31 is housed in the box unit 30 and it is constituted of a magnetic substance, then the rotational blurring of the roller 31 is prevented by the magnet 41. The roller 31 rotates clockwise to carry the developer to a developing action part in the center of a slit-like aperture part 26. At such a time, the roller 31 is attracted by the magnet 41 and rubs and rotates to the roller position regulating surface so as to be positioned. Since it is good for the roller 31 to be curved, a developing head in which the diameter of the roller is made small and which is miniaturized and lightened is realized. Then, the work to the roller 31 is simplified and the inexpensive developing head is realized. Since the developing itself has an action for removing and drying the developer, the auxiliary facility related to the development is simplified.