A power conversion device comprising: an AC converting unit configured to perform power conversion; and a calculating unit configured to control the AC converting unit, wherein the calculating unit includes a period converting unit configured to convert an input signal into a period signal, a period calculating unit configured to calculate an acquired frequency f from the period signal, and a control unit configured to output an output command according to the acquired frequency f, and in a case where the period signal is not acquirable during a period longer than a period of the period signal acquired from the period converting unit at a preceding time, the period calculating unit is configured to calculate a time period during which the period signal is not acquirable, and output the time period as the acquired frequency, characterized in that at a time point, when a period from the rising of a pulse at the preceding time to the falling of the pulse is set to Tpre and a predetermined time Tover has elapsed after the elapse of Tpre, the period calculating unit is configured to calculate the frequency f by the following equation and predict a pulse train input command of a low frequency before acquiring pulse edges: f = 1 / 2 × Tpre + Tover, wherein in a case where a current period input is longer than its previous period input, the acquired frequency is updated such that the acquired frequency decreases before an edge of the current period input arrives, so that it is possible to make a timing of updating the acquired frequency early. an AC converting unit configured to perform power conversion; and a calculating unit configured to control the AC converting unit, wherein the calculating unit includes a period converting unit configured to convert an input signal into a period signal, a period calculating unit configured to calculate an acquired frequency f from the period signal, and a control unit configured to output an output command according to the acquired frequency f, and in a case where the period signal is not acquirable during a period longer than a period of the period signal acquired from the period converting unit at a preceding time, the period calculating unit is configured to calculate a time period during which the period signal is not acquirable, and output the time period as the acquired frequency, characterized in that at a time point, when a period from the rising of a pulse at the preceding time to the falling of the pulse is set to Tpre and a predetermined time Tover has elapsed after the elapse of Tpre, the period calculating unit is configured to calculate the frequency f by the following equation and predict a pulse train input command of a low frequency before acquiring pulse edges: f = 1 / 2 × Tpre + Tover, a period converting unit configured to convert an input signal into a period signal, a period calculating unit configured to calculate an acquired frequency f from the period signal, and a control unit configured to output an output command according to the acquired frequency f, and in a case where the period signal is not acquirable during a period longer than a period of the period signal acquired from the period converting unit at a preceding time, the period calculating unit is configured to calculate a time period during which the period signal is not acquirable, and output the time period as the acquired frequency, characterized in that at a time point, when a period from the rising of a pulse at the preceding time to the falling of the pulse is set to Tpre and a predetermined time Tover has elapsed after the elapse of Tpre, the period calculating unit is configured to calculate the frequency f by the following equation and predict a pulse train input command of a low frequency before acquiring pulse edges: f = 1 / 2 × Tpre + Tover,