Provided is a heat pump heating system that can improve heat pump efficiency and heating capacity. The heat pump heating system comprises: a compressor that compresses a coolant; a heat exchanger that exchanges heat between the coolant compressed by the compressor and a liquid; a pump that causes the liquid to circulate between the heat exchanger and a heater; a first temperature sensor that detects an outgoing temperature, which is the temperature of the liquid being sent out to the heater from the heat exchanger; a second temperature sensor that detects a return temperature, which is the temperature of the liquid returning to the heat exchanger from the heater; and a control device that controls a circulation flow rate of the liquid such that the difference between the outgoing temperature and the return temperature in the case where the outgoing temperature is higher than a threshold becomes equal to or less than the difference between the outgoing temperature and the return temperature in the case where the outgoing temperature is equal to the threshold.
