A processor, an out-of-head localization filter generation method, and a program capable of performing appropriate processing are provided. An out-of-head localization filter determination device according to this embodiment includes a built-in microphone embedded in an output unit, a measurement unit configured to output a measurement signal to the output unit and measure a sound pickup signal output from the built-in microphone, a frequency characteristics acquisition unit configured to convert the sound pickup signal into a frequency domain and acquire first frequency characteristics, a conversion unit configured to convert the first frequency characteristics into second frequency characteristics by applying a representative conversion function to the first frequency characteristics, and an inverse filter calculation unit configured to calculate an inverse filter based on the second frequency characteristics.