PURPOSE: To position an optical element easily without using an electric means, by forming a photoreceptor used as a recording medium into a shape like a drum supported rotatably and providing an image forming optical system so as to face this photoreceptor.

CONSTITUTION: A photoreceptor 6 used as a recording device is formed into a shape like a drum supported rotatably, and an image forming optical system 20 is arranged so as to face the photoreceptor 6. Aperture parts 21 and 22 are provided in the upper part of the optical system 20 and the part of the optical system 20 facing the photoreceptor 6, and a lens array 24, a roof mirror array 25, a mirror 26, etc. are arranged in a case 23. The lens array 24 consists of plural lenses 27 and 28 which are arranged in the first and the second lines, respectively, and lenses 27 and 28 are arranged at approximately equal pitches. Arrays 30 are arranged in a line in positions facing pairs 29 of adjacent lenses 27 and 28. The pitch of arrays 30 is set to a value approximately equal to that beween lenses 27 and 28, and thus, the optical element is positioned easily without an electric means.