The present invention provides precise temperature control of a cooling chamber and comprises: a cooling chamber; a refrigeration circuit having a compressor, a condenser installed at the outlet side of the compressor, an evaporator, installed between the outlet side of the condenser and the inlet side of the compressor, for cooling the cooling chamber, and a decompression means installed at the inlet side of the evaporator; and a refrigerant control unit which has a refrigerant control valve installed between the condenser and the evaporator, and which adjusts the refrigerant flow rate that flows into the evaporator by controlling the opening/closing time of the refrigerant control valve.