the first mirror 19 in this operation the optical axis is coincident with the rotary axis of the rotary disk 18 the light beam 2 reflected by the first mirror 19 is reflected by the second mirror 20 which is fixedly secured in such a manner as to turn together with the first mirror 19 as a result of which the light beam 2 thus reflected is applied to one of the hologram lenses 6 on the hologram disk 7 the light beam is diffracted by the hologram lens 6 thus reaching the reading window 12 the light beam 15 scattered by the bar code on a label on the reading window 12 advances along the optical path of the light beam 2 in the opposite direction to reach the mirror 5 where it is reflected the light beam 15 thus reflected is applied through the condenser lens 21 to the photo detector 16 where it is converted into an electrical signal as seen from fig2 the mirror 29 and mirror 20 are fixed to the rotary disk 18 at predetermined angles such that light beam 2 passing through aperature 5a of mirror 5 is reflected from mirror 19 to mirror 20 and from mirror 20 through apearature 18a in addition the selected angles for mirrors 19 20 are such as to assure the reflections of light beam 15 from mirror 20 to mirror 18 and then to mirror 5 for reflection through lens 21 to photo detector 16 now the case where the hologram disk 7 and the rotary disk 18 are turned will be described first the hologram disk 7 is for example rotated at 5 000 r p m by the motor 17 similarly as in the above described case the light beam 2.