A deviation calculating unit 42 calculates a deviation between an internal temperature detected by a temperature sensor 35 and a target temperature provided from a target temperature setting unit 41 for each predetermined time period. The deviation is integrated by a deviation integrating unit 46. When the integrated value exceeds a predetermined reference value, a rotational speed of an inverter motor that drives a compressor is increased. Therefore, for example, even if an internal temperature temporarily rises because a door is opened temporarily and outside air flows into a storage compartment, because there is no sudden change in the integrated value of the temperature deviation and the rotational speed of the compressor does not react in an oversensitive manner and rapidly increase. Consequently the control is stable. Thus, an unnecessarily oversensitive response to a sudden change in an internal temperature can be prevented, enabling operation at a higher efficiency.