A printer comprising a cover, and a stacker that is attached to the cover, the stacker being supported pivotably about a pivot axis on the cover between a protruding position where the stacker receives paper discharged from the printer, and a retracted position rotated a predetermined angle from the protruding position. In order to achieve the object, a residue vector is generated by using an inverse filter from a difference vector outputted from a first differencer. The environmental defense shield serves to protect the engine from debris while also smoothing airflow into the engine.