PURPOSE: To achieve an air conditioning in which both heating and cooling are felt comfortable by differentiating the minimum rotational speed for the cooling operation from the minimum rotational speed for the heating operation so that the minimum speed for the cooling operation may be lower than the minimum speed for the heating operation.

CONSTITUTION: For the rotational speed for the heating operation, the minimum rotational speed (2,000rpm, for example) is set with a criterion in which the air temperature blown into the room is 37W38°C when the outside temperature is 0°C and the room temperature is 21°C. It will be perfect if a thermistor is installed near to an air outlet, which is inputted to a microcomputer through a comparator etc. to control the minimum rotational speed. For the cooling operation, on the other hand, the minimum rotational speed is set as low as possible. That is, in the cooling operation, the intermittent operation will cause the change in the room temperature as well as humidity, which is detrimental to the pleasantness. Therefore, by continuing the operation at a lowest possible speed (1,000rpm, for example) to continue dehumidifying, the comfortable feeling can be maintained.