A heat source machine including a heat pump cycle in which a compressor , a first heat exchanger (32;36), and a second heat exchanger (36;32) are arranged, the heat source machine arranged to perform, in the second heat exchanger (36;32), heat exchange between a heat medium supplied from an external load and a refrigerant to thereby cool or heat the heat medium to a predetermined set outlet temperature and to supply the cooled or heated heat medium to the external load , the heat source machine comprising: a data acquiring unit configured to acquire measurement values measured by various sensors such as an outlet temperature (Tout) of the heat medium, an inlet temperature (Tin) of the heat medium, a flow rate (F1) of the heat medium, an inlet temperature (Tcin) of a heat source supplied to the first heat exchanger (32;36), a flow rate (F2) of the heat source; a computing unit configured to calculate an evaluation value on a fluctuation for a parameter that influences the outlet temperature (Tout) of the heat medium using an arithmetic expression held in advance, the parameter being at least any one of the inlet temperature (Tin) of the heat medium, the flow rate (F1) of the heat medium, the inlet temperature (Tcin) of the heat source supplied to the first heat exchanger (32;36), the flow rate (F2) of the heat source, and a heat source machine load rate; and a set temperature changing unit configured to change the set outlet temperature of the heat medium so as to suppress a change in the outlet temperature (Tout) of the heat medium, in a case where the evaluation value calculated by the computing unit exceeds a predetermined threshold value, wherein the set temperature changing unit is arranged to decrease the set outlet temperature of the heat medium by a predetermined amount in a case where the outlet temperature (Tout) of the heat medium is on a rising trend, and to increase the set outlet temperature of the heat medium by a predetermined amount in a case where the outlet temperature (Tout) of the heat medium is on a falling trend. a data acquiring unit configured to acquire measurement values measured by various sensors such as an outlet temperature (Tout) of the heat medium, an inlet temperature (Tin) of the heat medium, a flow rate (F1) of the heat medium, an inlet temperature (Tcin) of a heat source supplied to the first heat exchanger (32;36), a flow rate (F2) of the heat source; a computing unit configured to calculate an evaluation value on a fluctuation for a parameter that influences the outlet temperature (Tout) of the heat medium using an arithmetic expression held in advance, the parameter being at least any one of the inlet temperature (Tin) of the heat medium, the flow rate (F1) of the heat medium, the inlet temperature (Tcin) of the heat source supplied to the first heat exchanger (32;36), the flow rate (F2) of the heat source, and a heat source machine load rate; and a set temperature changing unit configured to change the set outlet temperature of the heat medium so as to suppress a change in the outlet temperature (Tout) of the heat medium, in a case where the evaluation value calculated by the computing unit exceeds a predetermined threshold value, wherein the set temperature changing unit is arranged to decrease the set outlet temperature of the heat medium by a predetermined amount in a case where the outlet temperature (Tout) of the heat medium is on a rising trend, and to increase the set outlet temperature of the heat medium by a predetermined amount in a case where the outlet temperature (Tout) of the heat medium is on a falling trend. <EOS>