Provided is a construction machine in which the weight of a top plate of an aftertreatment device mount is reduced without reducing the rigidity of the top plate. In a construction machine (1) where avehicle body frame (5) for mounting an engine is equipped with an aftertreatment device mount (11) for supporting an exhaust gas aftertreatment device (10), a mount top plate (12) of the aftertreatment device mount (11) includes a support (20) on which the exhaust gas aftertreatment device (10) is placed, a pair of outer walls (21) extending parallel, a groove portion (22) parallel to the outerwalls (21), a connecting portion (23) provided on the support (20), and an upper reinforcing member (15) orthogonal to the groove portion at a position of the connecting portion (23). The upper reinforcing member (15) includes a first reinforcing portion (15a) for reinforcing the connecting portion (23) and a second reinforcing portion (15b) to be fitted in the groove portion (22).