A system includes an air conditioning device with a heat exchanger that sends conditioned air to an air conditioned space, a ventilation device that ventilates the air conditioned space, a refrigerant sensor that detects a concentration of a refrigerant in the air conditioned space, and a control unit that controls operations of the air conditioning device and ventilation device. On determination that the refrigerant concentration acquired from the refrigerant sensor exceeds a first predetermined value, the control unit sets an operation of a compressor of the air conditioning device to a stop state and sets the ventilation device to an operating state. On determination that the refrigerant concentration that has exceeded the first predetermined value becomes equal to or less than the first predetermined value, the control unit continues the stop state of the compressor and operating state of the ventilation device until a predetermined timing.