An optical apparatus for irradiating a surface to be scanned with laser light comprises rotary deflecting means for deflecting laser light emitted by a laser emitting means in a shape of a plane, a mirror for reflecting the laser light, an enclosure for housing the mirror, a first mirror supporting part capable of moving in a direction parallel to the laser light irradiated toward the mirror and supporting the mirror; and a second mirror supporting part capable of supporting the mirror in such a way that the mirror can rotate around an axis where the laser light is in close agreement with a scanning line with which the mirror is scanned.