CONSTRUCTION MACHINE

In a NOx selective catalytic reduction device that purifies NOx in exhaust gas exhausted from an engine (10), a urea water supply system is constructed of a urea water injection valve (20), a urea water tank (24), urea water supply piping (22) and a urea water supply device (30), a connection frame member (3d) is provided on a revolving superstructure (2, 3) to extend in a longitudinal direction in a center in a width direction to reinforce the revolving superstructure and to be located between a pair of main frame members (3b, 3b) that connects a working device (4) so that a rear side faces the engine, the urea water tank is placed on the revolving superstructure on a front side from a center of revolution of the revolving superstructure, the engine is placed on the revolving superstructure on a rear side from the center of revolution of the revolving superstructure, and the urea water supply device (30) is installed on the connection frame member (3d) to face the engine.