A hot water boiling apparatus includes a hot water storage tank (11). The storage tank has an inner tank (12) storing water therein, an outer tank (13) surrounding the inner trank, and a vacuum heat insula­tion layer (14) defined between the inner and outer tanks and surrounding the inner tank. A water flow type heating unit (22) is arranged outside the storage tank and used for drawing water from the inner tank through a water supply port (15) formed at the bottom of the inner tank and, after heating the water, supplying it into the inner tank through a hot water supply port (18) formed at the top of the inner tank. The unit includes a con­necting pipe (30, 33) one end of which is liquid tightly connected to the water supply port and passes through the outer tank in airtight fashion, and the other end of which is liquid tightly connected to the hot water supply port and passes through the outer tank in air­tight fashion.