A hybrid construction machine comprising: a swing structure; a hydraulic pump; a hydraulic swing motor driving the swing structure using hydraulic fluid from the hydraulic pump; an electric swing motor driving the swing structure in conjunction with the hydraulic swing motor; a hydraulic actuator operated simultaneously with the swing structure at times and driven by the hydraulic fluid from the hydraulic pump; a swing operating device for operating a swing operation of the swing structure; a directional control valve for meter-in control which valve is configured to be switched by the swing operating device and control flow of the hydraulic fluid supplied from the hydraulic pump to the hydraulic swing motor; a directional control valve for meter-out control which valve is configured to be switched by the swing operating device and control the flow of the hydraulic fluid returning from the hydraulic swing motor; and a regulating device (13, 30, 31) regulating operation of the directional control valve for meter-in control; characterized in that the regulating device (13, 30, 31) is configured to, during combined swing operation in which the hydraulic actuator is operated simultaneously with the swing structure, prevent the switching operation of the directional control valve for meter-in control by the swing operation device to cause the swing structure to be driven by the electric swing motor alone, and the directional control valve for meter-out control is configured to, even while the switching operation of the directional control valve for meter-in control is prevented by the regulating device (13, 30, 31), be switched by the swing operating device and control the flow of the hydraulic fluid returning from the hydraulic swing motor. a swing structure; a hydraulic pump; a hydraulic swing motor driving the swing structure using hydraulic fluid from the hydraulic pump; an electric swing motor driving the swing structure in conjunction with the hydraulic swing motor; a hydraulic actuator operated simultaneously with the swing structure at times and driven by the hydraulic fluid from the hydraulic pump; a swing operating device for operating a swing operation of the swing structure; a directional control valve for meter-in control which valve is configured to be switched by the swing operating device and control flow of the hydraulic fluid supplied from the hydraulic pump to the hydraulic swing motor; a directional control valve for meter-out control which valve is configured to be switched by the swing operating device and control the flow of the hydraulic fluid returning from the hydraulic swing motor; and a regulating device (13, 30, 31) regulating operation of the directional control valve for meter-in control; characterized in that the regulating device (13, 30, 31) is configured to, during combined swing operation in which the hydraulic actuator is operated simultaneously with the swing structure, prevent the switching operation of the directional control valve for meter-in control by the swing operation device to cause the swing structure to be driven by the electric swing motor alone, and the directional control valve for meter-out control is configured to, even while the switching operation of the directional control valve for meter-in control is prevented by the regulating device (13, 30, 31), be switched by the swing operating device and control the flow of the hydraulic fluid returning from the hydraulic swing motor.