A construction machine that permits an exhaust gas after-treatment device to be disposed while suppressing an increase of height. An upper surface of a hydraulic pump is positioned lower than an upper surface of an engine, a tank device having at least one of a working oil tank and a fuel tank is provided at a rear portion thereof with a small height portion which has an upper surface of a height almost equal to or smaller than the height of the upper surface of the hydraulic tank, and an exhaust gas after-treatment device is disposed at a position above both the small height portion and the hydraulic pump.