CONSTRUCTION MACHINE

Disclosed is a construction machine including an additional control valve that connects a bottom-side hydraulic line and a tank-side hydraulic line to each other and connects a rod-side hydraulic line and the tank-side hydraulic line to each other, the bottom-side hydraulic line connecting a bottom side of a hydraulic cylinder that drives a work device and a main control valve to each other, the rod-side hydraulic line connecting a rod side of the hydraulic cylinder and the main control valve to each other. The additional control valve includes a variable relief valve that is provided between the rod-side hydraulic line and the tank-side hydraulic line and that controls a pressure in the rod-side hydraulic line such that the pressure is equal to or lower than a predetermined target pressure, and a check valve that permits only a flow of a hydraulic fluid from the tank-side hydraulic line to the bottom-side hydraulic line. In a case a work mode is switched to a float mode in which work is performed using an own weight of the work device, a meter-in control valve of the main control valve is closed, the target pressure of the variable relief valve is set to the minimum value of a predetermined pressure range, and a hydraulic fluid in the rod-side hydraulic line is discharged into the hydraulic fluid tank. As a result, it is possible to increase operability at the time of float work while suppressing deterioration in control performance and pressure loss.