A color laser printer is provided with a first exhaust duct for exhausting ozone generated by a charging unit etc. inside a housing to the outside of the housing. The first exhaust duct is therein provided with a catalytic honeycomb filter for ozone gas treatment and an ion emitting unit for emitting negative ions into an atmosphere. Most of an ozone gas component is decomposed and/or absorbed by the catalytic honeycomb filter for ozone gas treatment. Furthermore, the residual ozone gas component is decomposed by the negative ions generated by the ion emitting unit. This arrangement makes it possible to provide a new ozone removal device which is different from an ozone decomposing filter or a heat source.