A modular data center comprising: an enclosure; a fan provided in the enclosure and configured to create a first cooling wind from outside air without changing a temperature of the outside air; an air conditioner provided in the enclosure and configured to create a second cooling wind having a temperature lower than the temperature of the outside air; a plurality of racks provided in the enclosure and configured to house a plurality of electronic devices each provided with an intake face to take in the first cooling wind and the second cooling wind; and a control unit configured to adjust an air volume of the first cooling wind by controlling the fan, and so as to cool a temperature of each electronic device to a specified temperature (T S), characterised in that the control unit is configured to execute: determining whether or not the air conditioner is stopped; when the air conditioner is determined to be not stopped, calculating a first assumed value (P 1) of the power assumed to be consumed by the fan in a case of cooling the temperature of each electronic device to the specified temperature (T S) by using the first cooling wind while the air conditioner is stopped; stopping the air conditioner when the first assumed value (P 1) is smaller than a current value (P 0) of a sum of the power consumed by the air conditioner and the power consumed by the fan; when the air conditioner is determined to be stopped, calculating a second assumed value (P 2) of a sum of the power assumed to be consumed by the air conditioner and the power assumed to be consumed by the fan in a case of cooling the temperature of each electronic device to the specified temperature (T S) by using the first cooling wind and the second cooling wind while operating the air conditioner; and operating the air conditioner when the second assumed value (P 2) is smaller than the current value (P 0). an enclosure; a fan provided in the enclosure and configured to create a first cooling wind from outside air without changing a temperature of the outside air; an air conditioner provided in the enclosure and configured to create a second cooling wind having a temperature lower than the temperature of the outside air; a plurality of racks provided in the enclosure and configured to house a plurality of electronic devices each provided with an intake face to take in the first cooling wind and the second cooling wind; and a control unit configured to adjust an air volume of the first cooling wind by controlling the fan, and so as to cool a temperature of each electronic device to a specified temperature (T S), characterised in that the control unit is configured to execute: determining whether or not the air conditioner is stopped; when the air conditioner is determined to be not stopped, calculating a first assumed value (P 1) of the power assumed to be consumed by the fan in a case of cooling the temperature of each electronic device to the specified temperature (T S) by using the first cooling wind while the air conditioner is stopped; stopping the air conditioner when the first assumed value (P 1) is smaller than a current value (P 0) of a sum of the power consumed by the air conditioner and the power consumed by the fan; when the air conditioner is determined to be stopped, calculating a second assumed value (P 2) of a sum of the power assumed to be consumed by the air conditioner and the power assumed to be consumed by the fan in a case of cooling the temperature of each electronic device to the specified temperature (T S) by using the first cooling wind and the second cooling wind while operating the air conditioner; and operating the air conditioner when the second assumed value (P 2) is smaller than the current value (P 0). determining whether or not the air conditioner is stopped; when the air conditioner is determined to be not stopped, calculating a first assumed value (P 1) of the power assumed to be consumed by the fan in a case of cooling the temperature of each electronic device to the specified temperature (T S) by using the first cooling wind while the air conditioner is stopped; stopping the air conditioner when the first assumed value (P 1) is smaller than a current value (P 0) of a sum of the power consumed by the air conditioner and the power consumed by the fan; when the air conditioner is determined to be stopped, calculating a second assumed value (P 2) of a sum of the power assumed to be consumed by the air conditioner and the power assumed to be consumed by the fan in a case of cooling the temperature of each electronic device to the specified temperature (T S) by using the first cooling wind and the second cooling wind while operating the air conditioner; and operating the air conditioner when the second assumed value (P 2) is smaller than the current value (P 0).