The out-of-head localization unit 10 includes convolution calculation units 11, 12, 21, and 22 that store spatial acoustic transfer characteristics Hls, Hlo, Hro, and Hrs, respectively, and adders 24 and 25. The convolution calculation units 11, 12, 21, and 22 perform convolution processing using the spatial acoustic transfer characteristics. The stereo input signals XL and XR from a CD player or the like are input to the out-of-head localization unit 10. The out-of-head localization unit 10 has the spatial acoustic transfer characteristics set therein. The out-of-head localization unit 10 convolves filters having the spatial acoustic transfer characteristics (hereinafter, also referred to as spatial acoustic filters) with each of the stereo input signals XL and XR on the respective channels. The spatial acoustic transfer characteristics may be a head-related transfer function HRTF measured on the head or auricle of a person being measured, or may be the head-related transfer function of a dummy head or a third person.

A set of the four spatial acoustic transfer characteristics Hls, Hlo, Hro, and Hrs is defined as a spatial acoustic transfer function. Data used for the convolution in the convolution calculation units 11, 12, 21, and 22 serve as the spatial acoustic filters. A spatial acoustic filter is generated by cutting out each of the spatial acoustic transfer characteristics Hls, Hlo, Hro, and Hrs with a specified filter length.