The heat supply system (1) according to one aspect of the present invention comprises: a cushion tank (20) provided in an outbound pipe (11); a first heat source machine (30) that has a steam compression heat pump (31) and heats circulating water circulating in the outbound pipe (11) upstream of the cushion tank (20); a second heat source machine (40) that has a combustion boiler (41) and heats the circulating water circulating in the outbound pipe (11) upstream of the cushion tank (20); a return temperature detection means (91) for detecting the return temperature Tr of the circulating water sent back from a heat load part (14, 15) through a return pipe (13); a first control means (60) for controlling the operation of the first heat source machine (30) on the basis of the return temperature Tr; and a second control means (80) for controlling the operation of the second heat source machine (40) on the basis of the return temperature Tr.