To achieve a lower cost and a smaller size of a controller while saving energy by curtailing a power due to a loss of an inverter when a load is large.

A pressure sensor 11 is provided between a compressor 3 and an evaporator 6 and a current sensor 12 is provided at an input of a drive motor 19 of the compressor 3. The pressure sensor 11 transmits a suction pressure of a refrigerant gas detected in real time at an time interval and an input current value of the drive motor 19 to a control unit 15. The control unit 15 organizes a program to correct a cooling capacity control signal gradually in a real time treatment by applying a feedback to the cooling capacity control signal using a deviation of the suction pressure of the refrigerant gas from a target pressure as reference to input the resulting cooling capacity control signal into an inverter 16. When an input current of the drive motor 19 is larger than a changeover current value set by a changeover current setting 14, the drive motor 19 is driven by a direct 3-phase AC power source or when it is smaller, the drive motor 19 is driven by the inverter 16.