The present invention provides a method of producing a cell mass capable of serving as a primitive organ-like structure comprised of a plurality of somatic cell types of somatic origin, comprising: preparing cultures containing the plurality of types of somatic cells; mixing the plurality of types of somatic cell cultures followed by adding a Wnt signal activator to the mixed cell culture; subjecting the culture containing the Wnt signal activator to non-plate contact culturing over a predetermined time period; and replacing the medium of the culture cultured by the non-plate contact culturing with medium not containing Wnt signal activator and further culturing for a predetermined time period; wherein, at least one type of the plurality of somatic cells is maintained in an undifferentiated state.