A construction machine, comprising: a revolving superstructure (2, 3); an operator's cab provided at a front part on the revolving superstructure (2, 3); a working device mounting section provided at the front part on the revolving superstructure (2, 3) in a side part of the operator's cab; a counterweight provided at a rear part of the revolving superstructure (2, 3); an engine as a drive source placed on the revolving superstructure (2, 3) between the counterweight and the operator's cab; a NOx selective catalytic reduction device installed on a side of the engine and interposed in an exhaust passage of the engine; a urea water injection valve that injects urea water to exhaust upstream of the NOx selective catalytic reduction device; a urea water tank that stores the urea water; urea water supply piping with one end connected to the urea water injection valve, and the other end connected to the urea water tank; and a urea water supply device that is interposed in the urea water supply piping, and feeds the urea water under pressure to the urea water injection valve, the urea water tank is placed on the revolving superstructure (2, 3) on a front side from a center of revolution of the revolving superstructure (2, 3), the engine is placed on the revolving superstructure (2, 3) on a rear side from the center of revolution of the revolving superstructure (2, 3), the revolving superstructure (2, 3) has a pair of main frame members that extend in a longitudinal direction near a center in a width direction to reinforce the revolving superstructure (2, 3) and construct the working device mounting section, characterized in that a connection frame member that connects the pair of main frame members between the center of revolution of the revolving superstructure (2, 3) and the engine, and the urea water supply device is installed on the connection frame member to face the engine. a revolving superstructure (2, 3); an operator's cab provided at a front part on the revolving superstructure (2, 3); a working device mounting section provided at the front part on the revolving superstructure (2, 3) in a side part of the operator's cab; a counterweight provided at a rear part of the revolving superstructure (2, 3); an engine as a drive source placed on the revolving superstructure (2, 3) between the counterweight and the operator's cab; a NOx selective catalytic reduction device installed on a side of the engine and interposed in an exhaust passage of the engine; a urea water injection valve that injects urea water to exhaust upstream of the NOx selective catalytic reduction device; a urea water tank that stores the urea water; urea water supply piping with one end connected to the urea water injection valve, and the other end connected to the urea water tank; and a urea water supply device that is interposed in the urea water supply piping, and feeds the urea water under pressure to the urea water injection valve, the urea water tank is placed on the revolving superstructure (2, 3) on a front side from a center of revolution of the revolving superstructure (2, 3), the engine is placed on the revolving superstructure (2, 3) on a rear side from the center of revolution of the revolving superstructure (2, 3), the revolving superstructure (2, 3) has a pair of main frame members that extend in a longitudinal direction near a center in a width direction to reinforce the revolving superstructure (2, 3) and construct the working device mounting section, characterized in that a connection frame member that connects the pair of main frame members between the center of revolution of the revolving superstructure (2, 3) and the engine, and the urea water supply device is installed on the connection frame member to face the engine.