A construction machine that permits an exhaust gas after-treatment device to be disposed while avoiding an increase of height and hence avoiding narrowing of an operator's visual field. A guard panel is disposed substantially in parallel with a base frame. The guard panel includes a top plate, the top plate including an opening formed at a portion thereof corresponding to an engine, and a bonnet formed so as to project upwards from the top plate and cover the opening. A first treatment section is disposed lower than the top plate and a second treatment section includes at least a portion positioned higher than the top plate through the opening and lower than the bonnet.