A storage unit of a time-series data accumulation device of an embodiment stores statistical value data. A determination unit determines an interval function on the basis of data capacity, and a total amount of time elapsed from the beginning of measurement of a time-series data. A first calculation unit calculates an interval indicating an amount of time required to measure all the time-series data items constituting desired statistical value data on the basis of the determined interval function. A second calculation unit acquires all the time-series data items on the basis of the calculated interval, and thereafter calculates the statistical value on the basis of all the acquired time-series data items. A write unit writes the calculated statistical value to the storage unit as the statistical value data.