A power conversion device for converting a DC or AC input voltage to a voltage having arbitrary frequency, the power conversion device characterized by comprising: a linear function conversion unit configured to convert a detected or estimated electric signal to a linear function representing a time displacement of phase of the electric signal; a gradient extraction unit configured to extract a gradient from the linear function converted by the linear function conversion unit; an intercept extraction unit configured to extract an intercept from the linear function converted by the linear function conversion unit and the gradient extracted by the gradient extraction unit, wherein the intercept represents the size of the phase at a time detection is started; a filter processing unit comprising at least either a gradient filter processing unit configured to perform filter processing on the gradient extracted by the gradient extraction unit or an intercept filter processing unit configured to perform filter processing on the intercept extracted by the intercept extraction unit; a linear function inverse conversion unit configured to regain a linear function, using the gradient on which the filter processing has been performed by the gradient filter processing unit and the intercept on which the filter processing has been performed by the intercept filter processing unit in a case where the filter processing unit comprises the gradient filter processing unit and the intercept filter processing unit, or using the gradient or the intercept on which the filter processing has been performed by the gradient filter processing unit or the intercept filter processing unit and the gradient or the intercept extracted by the gradient extraction unit or the intercept extraction unit as gradient or intercept on which the filter processing has not been performed in a case where the filter processing unit comprises the gradient filter processing unit or the intercept filter processing unit; and a phase inverse conversion unit configured to return the linear function inversely converted by the linear function inverse conversion unit to a time displacement of the phase, wherein an output voltage of the power conversion device is controlled using a inversely converted phase that is inversely converted by the phase inverse conversion unit. a linear function conversion unit configured to convert a detected or estimated electric signal to a linear function representing a time displacement of phase of the electric signal; a gradient extraction unit configured to extract a gradient from the linear function converted by the linear function conversion unit; an intercept extraction unit configured to extract an intercept from the linear function converted by the linear function conversion unit and the gradient extracted by the gradient extraction unit, wherein the intercept represents the size of the phase at a time detection is started; a filter processing unit comprising at least either a gradient filter processing unit configured to perform filter processing on the gradient extracted by the gradient extraction unit or an intercept filter processing unit configured to perform filter processing on the intercept extracted by the intercept extraction unit; a linear function inverse conversion unit configured to regain a linear function, using the gradient on which the filter processing has been performed by the gradient filter processing unit and the intercept on which the filter processing has been performed by the intercept filter processing unit in a case where the filter processing unit comprises the gradient filter processing unit and the intercept filter processing unit, or using the gradient or the intercept on which the filter processing has been performed by the gradient filter processing unit or the intercept filter processing unit and the gradient or the intercept extracted by the gradient extraction unit or the intercept extraction unit as gradient or intercept on which the filter processing has not been performed in a case where the filter processing unit comprises the gradient filter processing unit or the intercept filter processing unit; and a phase inverse conversion unit configured to return the linear function inversely converted by the linear function inverse conversion unit to a time displacement of the phase, wherein an output voltage of the power conversion device is controlled using a inversely converted phase that is inversely converted by the phase inverse conversion unit.