A power measurement device, comprising: a first three-phase to two-phase converter converting a three-phase voltage signal of three-phase alternating current power into a two-phase voltage signal; a second three-phase to two-phase converter converting a three-phase current signal of the three-phase alternating current power into a two-phase current signal; an instantaneous power calculator calculating an instantaneous value of active power of the three-phase alternating current power and an instantaneous value of reactive power of the three-phase alternating current power based on the two-phase voltage signal and the two-phase current signal; characterised by: a first moving average calculator including a plurality of first moving average filters calculating moving averages, the plurality of first moving average filters using different data quantities, the first moving average calculator causing the plurality of first moving average filters to respectively calculate a plurality of active power average values of different moving average data quantities; a second moving average calculator including a plurality of second moving average filters calculating moving averages, the plurality of second moving average filters using different data quantities, the second moving average calculator causing the plurality of second moving average filters to respectively calculate a plurality of reactive power average values of different moving average data quantities; a first average value calculator calculating an average value of the active power corresponding to a frequency of the three-phase alternating current power based on the plurality of active power average values and frequency information representing the frequency of the three-phase alternating current power; and a second average value calculator calculating an average value of the reactive power corresponding to the frequency of the three-phase alternating current power based on the plurality of reactive power average values and the frequency information representing the frequency of the three-phase alternating current power. a first three-phase to two-phase converter converting a three-phase voltage signal of three-phase alternating current power into a two-phase voltage signal; a second three-phase to two-phase converter converting a three-phase current signal of the three-phase alternating current power into a two-phase current signal; an instantaneous power calculator calculating an instantaneous value of active power of the three-phase alternating current power and an instantaneous value of reactive power of the three-phase alternating current power based on the two-phase voltage signal and the two-phase current signal; characterised by: a first moving average calculator including a plurality of first moving average filters calculating moving averages, the plurality of first moving average filters using different data quantities, the first moving average calculator causing the plurality of first moving average filters to respectively calculate a plurality of active power average values of different moving average data quantities; a second moving average calculator including a plurality of second moving average filters calculating moving averages, the plurality of second moving average filters using different data quantities, the second moving average calculator causing the plurality of second moving average filters to respectively calculate a plurality of reactive power average values of different moving average data quantities; a first average value calculator calculating an average value of the active power corresponding to a frequency of the three-phase alternating current power based on the plurality of active power average values and frequency information representing the frequency of the three-phase alternating current power; and a second average value calculator calculating an average value of the reactive power corresponding to the frequency of the three-phase alternating current power based on the plurality of reactive power average values and the frequency information representing the frequency of the three-phase alternating current power. a first moving average calculator including a plurality of first moving average filters calculating moving averages, the plurality of first moving average filters using different data quantities, the first moving average calculator causing the plurality of first moving average filters to respectively calculate a plurality of active power average values of different moving average data quantities; a second moving average calculator including a plurality of second moving average filters calculating moving averages, the plurality of second moving average filters using different data quantities, the second moving average calculator causing the plurality of second moving average filters to respectively calculate a plurality of reactive power average values of different moving average data quantities; a first average value calculator calculating an average value of the active power corresponding to a frequency of the three-phase alternating current power based on the plurality of active power average values and frequency information representing the frequency of the three-phase alternating current power; and a second average value calculator calculating an average value of the reactive power corresponding to the frequency of the three-phase alternating current power based on the plurality of reactive power average values and the frequency information representing the frequency of the three-phase alternating current power.