A construction machine, comprising: a lower travelling body; an upper slewing body mounted on the lower travelling body to be slewable around a vertical axis, the upper slewing body including an upper frame, the upper frame including a bottom plate and a floor plate disposed over the bottom plate with a distance; an operation seat being provided on the upper frame; a plurality of hydraulic actuators; a control valve assembly which is an assembly of control valves configured to control respective actuations of the hydraulic actuators, respectively, the control valve assembly being provided in an underfloor space between the bottom plate and the floor plate; a plurality of remote control valves for operating the control valves, respectively; an operation-pattern selector valve provided in the underfloor space for selecting an operation pattern of combinations between the remote control valves and the control valves, the operation-pattern selector valve including a tubular body, a shaft held in the body rotatably around an axis of the shaft, a handle for switching operation, the handle extending from one end of the shaft in a direction orthogonal to the axis of the shaft, and a plurality of remote-control-hose connection ports; a partition wall provided to stand upright on the bottom plate at a rear side of the control valve assembly; a plurality of remote control hoses which are connected to the respective remote-control-hose connection ports to which connect the remote control valves to the operation-pattern selector valve, respectively; a plurality of pilot hoses which connect the control valves to the operation-pattern selector valve, respectively; and a plurality of actuator hoses which connect the control valves to the hydraulic actuators, respectively; characterized by the remote control hose connection ports being disposed higher than an upper surface of the control valve assembly, a valve mounting member disposed on the bottom plate, the control valve assembly and the operation-pattern selector valve being mounted on the common valve mounting member; a bracket having a lower end connected to the front end of the valve mounting member and an upper portion to which the operation-pattern selector valve is fixed, the operation-pattern selector valve being mounted on the valve mounting member via the bracket in a horizontal posture where the shaft extends horizontally, at a front side of the control valve assembly as viewed from an operator seated on the operation seat. a lower travelling body; an upper slewing body mounted on the lower travelling body to be slewable around a vertical axis, the upper slewing body including an upper frame, the upper frame including a bottom plate and a floor plate disposed over the bottom plate with a distance; an operation seat being provided on the upper frame; a plurality of hydraulic actuators; a control valve assembly which is an assembly of control valves configured to control respective actuations of the hydraulic actuators, respectively, the control valve assembly being provided in an underfloor space between the bottom plate and the floor plate; a plurality of remote control valves for operating the control valves, respectively; an operation-pattern selector valve provided in the underfloor space for selecting an operation pattern of combinations between the remote control valves and the control valves, the operation-pattern selector valve including a tubular body, a shaft held in the body rotatably around an axis of the shaft, a handle for switching operation, the handle extending from one end of the shaft in a direction orthogonal to the axis of the shaft, and a plurality of remote-control-hose connection ports; a partition wall provided to stand upright on the bottom plate at a rear side of the control valve assembly; a plurality of remote control hoses which are connected to the respective remote-control-hose connection ports to which connect the remote control valves to the operation-pattern selector valve, respectively; a plurality of pilot hoses which connect the control valves to the operation-pattern selector valve, respectively; and a plurality of actuator hoses which connect the control valves to the hydraulic actuators, respectively; characterized by the remote control hose connection ports being disposed higher than an upper surface of the control valve assembly, a valve mounting member disposed on the bottom plate, the control valve assembly and the operation-pattern selector valve being mounted on the common valve mounting member; a bracket having a lower end connected to the front end of the valve mounting member and an upper portion to which the operation-pattern selector valve is fixed, the operation-pattern selector valve being mounted on the valve mounting member via the bracket in a horizontal posture where the shaft extends horizontally, at a front side of the control valve assembly as viewed from an operator seated on the operation seat.