A scanning optical system comprises: a light source which emits a beam of light; a deflecting system that dynamically deflects the beam emitted by the light source with its deflecting surface; and a scan lens group including a molded resin lens, which focuses the beam dynamically deflected and scanned in a main scanning direction by the deflecting system on an image formation surface. The dielectric multilayered film includes a first period layer with a structure represented by a formula n and a second period layer with a structure represented by a formula m. Briefly stated, code is created that executes in a common execution environment. The processing unit is capable of analyzing the rhythm of music and commanding the illuminating object to flash based on the music.