To provide a writing optical device which is capable of efficiently cooling a rotary scanner without degrading its soundproof and dustproof performance by assuring the hermeticity of an optical housing for housing the rotary scanner and an image forming device mounted with this device.

The base surface of the optical housing (2) for housing the rotary scanner (1) is provided with an aperture (8) to enable the circulation of air in the optical housing (2), by which the heat generated by driving of the rotary scanner (1) is discharged.