To obtain a non-particle-aggregation-type organic polymer monolith separation medium, there is provided a monolith separation medium comprising a skeletal phase and pores being continuous in the form of three-dimensional network, which skeletal phase on its surface has a functional group permitting introduction of a new functional group. The skeletal phase has a non-particle-aggregation-type co-continuous structure having an average diameter of submicron to micrometer size, and is constituted of an addition polymer from an epoxy compound of bi- or higher functionality and an amine compound of bi- or higher functionality. Further, the skeletal phase is enriched in organic matter and does not contain any carbon atoms derived from aromatic series.