PURPOSE: To eliminate completely obstacles such as outflow of cold water at the time of opening of a water tap and a delay in supplying hot water, by winding a heat insulating component to be obtained by enclosing a latent heat accumulating material around an external circumferential surface of a hot water supply pipe extending to the water tap from a hot water supply device.

CONSTITUTION: A heat insulating component 5 formed by enclosing a latent heat accumulating material 4 such as paraffin between sheets made of heat resisting resin is wound around an external circumferential surface of a hot water supply pipe 3 extending toward a water tap 2 from a hot water supply device 1 extending along a whole length of the external circumferential surface of the hot water supply pipe. The latent heat accumulating material 4 is an article giving heat insulation effectiveness to hot water being stored within a hot water supply pipe 3 by making use of latent heat of fusion and it is desirable as physical and thermal properties that the fusion point is within a required operating temperature range, heat of fusion per volume is high, operation is done reliably and stably against repeatition of a cycle of fusion and solidification, thermal conductivity and growth rate of crystallization are high and a variation of volume and a thermal expansion coefficiency following on a variation of a phase are small.