To provide a hot water supply device capable of performing instantaneous hot-water supply and normal hot-water supply in safety by reliably determining the use of another tap.SOLUTION: Processing executed by a control device of a hot water supply device includes: a step (S510) for transferring an operation mode of the hot water supply device to an instantaneous hot-water supply mode; a step (S520) for measuring a water amount X flowing into a heat exchanger during an instantaneous hot-water circulation operation on the basis of a detection value of a water amount sensor; a step (S540) for determining occurrence of interruption by another tap in a case when the water amount X is a basic flow rate Y+α or more (YES in step S530); a step (S550) for stopping the operation of the circulation pump; a step (S570) for re-learning the water amount X in a case when the water amount X is less than the basic flow rate Y-β (YES in step S560); a step (S590) for terminating the instantaneous hot-water circulation mode in a case when a condition to terminate the instantaneous hot-water supply mode is established (YES in step S580); and a step (S520) for measuring the water amount X in a case when it is not established (NO in step S580).SELECTED DRAWING: Figure 5