PURPOSE: To carry out economical temperature control by making up the device of a pulse generating circuit, a medium temperature detecting means, a means for controlling the pulse width in response to the temperature of the medium, a medium circulating means that is controlled by the pulse width being output by the above pulse width control means, and a medium temperature changing means.

CONSTITUTION: On the basis of the information with regard to the temperature detected by a medium temperature detecting means 11, the pulse width generated by a pulse generating circuit 1 is changed by a pulse-width control means 2, and by applying a current corresponding to the change of the pulse width to a medium circulating means 14 such as a fan motor, the operating condition of the medium circulating means 14 is controlled. A control circuit 3 is constituted so that while monitoring the operating condition of the medium circulating means 14, when it is brought into a prescribed operating condition, a medium temperature changing means 19 such as a compressor or the like is brought into a driven or nondriven condition. In other words, the medium circulating function of the medium circulating means 14 is automatically changed in proportion to the medium temperature in the inside of the closed space, and also the medium temperature changing means 19 is automatically changed accordingly.