To provide a hot water supply unit which can supply hot water immediately upon demand at low cost.

A hot water supply line 3 is branched in the way by a branch line 4 being led to a heat exchanger 5. The branched hot water supply line is spiral in the heat exchanger 5 filled with high temperature hot water introduced from a high temperature hot water supply apparatus through a high temperature hot water supply line 6 and returned back to the high temperature hot water supply apparatus through a return line 7 to circulate. Hot water in the branched hot water supply line is heated up to a high temperature and mixed with hot water from the unbranched hot water supply line 3 through a mixing type three-way valve 8 before being fed to a water supply/hot water supply tap 1. Temperature of hot water mixed through the mixing type three- way valve 8 is detected by a temperature detector and the mixing type three- way valve 8 is operated through a temperature regulator (not shown) thus controlling the temperature of hot water mixed through the mixing type three- way valve 8 to a constant level.