To carefully control the surface potential of a photoreceptor by arranging plural light emitting elements on the opposite side of a substrate on which an optical writing head is constituted as a head for the photoreceptor.

Potential detecting electrodes 9 arranged on the photoreceptor side of a transparent substrate 8 having surface light emitting elements 10 on the opposite side are transparent electrodes consisting of ITOs and formed on the side facing the photoreceptor at 200μm/squ. The potential detecting electrodes 9 are formed at three places of the vicinities of both sides and the center on the image in the axial direction of the photoreceptor 1. These electrodes 9 are capacitively coupled to the photoreceptor 1 and connected to an amplifier not shown by a figure, through a lead wire, to output potential data to the control part of a printer. Moreover, a part of each detecting electrode constituting the lead wire is covered with insulating layers. When an electrophotographic printer having such a constitution is operated, the potential data from the potential detecting electrodes 9 can be surely obtained and the surface potential of the photoreceptor 1 can be partially controlled.