A multi-unit air conditioning system , comprising: an outdoor unit disposed in a first space; a plurality of indoor units configured to send an air to at least one second space different from the first space, the plurality of indoor units and the outdoor unit forming a refrigeration cycle; and a control device configured to control the plurality of indoor units , wherein each indoor unit among the plurality of indoor units includes a notification unit , each indoor unit is configured to cause the notification unit of the indoor unit to operate in response to a notification signal (Cm1, Cm2, Cm3) from the control device , and to transmit to the control device a response signal (Ac1, Ac2, Ac3, Ac3F) which includes identification information of the indoor unit, and an operational status of the notification unit of the indoor unit, the multi-unit air conditioning system is configured such that an operation of the notification unit can be checked by a user (Us1) who is in the at least one second space, the indoor units are configured such that, when at least one indoor unit included in the plurality of indoor units is malfunctioning, the at least one indoor unit each transmits to the control device a malfunction occurred signal (Ab3) which includes identification information of the indoor unit, characterized in that the control device is configured, when the control device cannot check the operation of the notification unit included in each of the at least one indoor unit by a response signal (Ac1, Ac2, Ac3, Ac3F) corresponding to the transmitted notification signal (Cm1, Cm2, Cm3), to transmit a notification signal (Cm1, Cm2, Cm3) to an indoor unit to which a notification signal (Cm1, Cm2, Cm3) has not been transmitted among the plurality of indoor units . an outdoor unit disposed in a first space; a plurality of indoor units configured to send an air to at least one second space different from the first space, the plurality of indoor units and the outdoor unit forming a refrigeration cycle; and a control device configured to control the plurality of indoor units , wherein each indoor unit among the plurality of indoor units includes a notification unit , each indoor unit is configured to cause the notification unit of the indoor unit to operate in response to a notification signal (Cm1, Cm2, Cm3) from the control device , and to transmit to the control device a response signal (Ac1, Ac2, Ac3, Ac3F) which includes identification information of the indoor unit, and an operational status of the notification unit of the indoor unit, the multi-unit air conditioning system is configured such that an operation of the notification unit can be checked by a user (Us1) who is in the at least one second space, the indoor units are configured such that, when at least one indoor unit included in the plurality of indoor units is malfunctioning, the at least one indoor unit each transmits to the control device a malfunction occurred signal (Ab3) which includes identification information of the indoor unit, characterized in that the control device is configured, when the control device cannot check the operation of the notification unit included in each of the at least one indoor unit by a response signal (Ac1, Ac2, Ac3, Ac3F) corresponding to the transmitted notification signal (Cm1, Cm2, Cm3), to transmit a notification signal (Cm1, Cm2, Cm3) to an indoor unit to which a notification signal (Cm1, Cm2, Cm3) has not been transmitted among the plurality of indoor units . <EOS>