A vehicle-mounted temperature controller has a first heat circuit and a refrigeration circuit. The first heat circuit has a first radiator exchanging heat with outside air, a first heat exchanger, and a first pump, and configured so that a first heat medium is circulated therethrough. The refrigeration circuit has the first heat exchanger discharging heat from the refrigerant to a first heat medium to make a refrigerant condense, a second heat exchanger absorbing heat to the refrigerant to thereby make the refrigerant evaporate and to cool an object to be cooled, and a compressor, and is configured so that the refrigerant circulates through the first heat exchanger and the second heat exchanger and thereby a refrigeration cycle is realized. When the object to be cooled starts being cooled, the compressor is started up after the first pump is started up.