PURPOSE: To avert the uneven scanning lines on a scanning plate owing to the deviation in a hologram rotating body at a low cost and with ease, by providing a means for correcting eccentricity which changes the course of light by a required quantity in the direction of compensating the deviation of the hologram rotating body.

CONSTITUTION: Tapered plates PL1WPL8 having light transmittability are disposed on the holograms formed on a hologram rotating body 10. These plates are tapered to the degrees of the tendency at which the deviations of the holograms corresponding to said plates are compensated. The plates PLs function as a kind of prism, wherein the relation =(θ1+θ'2)-σ holds if the vertical angle thereof is designated as σ, the angle of deviation as , the indicent angle as θ1, and the exit angle θ'2. When the width of the prism changes from l to l', the difference Δl thereof and the shift Δx in the course of the light have the relation Δx=Δltan. Therefore, the deviation in the optical path of the scanning light owing to the eccentricity of the hologram rotating body is corrected by adjusting and setting the width of the prism.