Electrostatic developing units are arranged in the record paper conveyance direction, form dot latent images in conformity with image dot data through the issue of scanning light on photosensitive drums in rotation, and after developing by toner components, transfer dots onto record paper for development. For each lighting noticeable dot amount image dot data, a quantity-of-light control unit provides control and output of optical energy of the noticeable dot on the basis of peripheral dots which may have influence on the size of the noticeable dot on the record paper, for example, in response to the distance from the peripheral dots.