To provide a new technique by which efficient transfection is ensured in delivering a target gene into a cell, disclosed is a nucleic acid construct for nuclear import, which comprises a ternary complex consisting of a nucleic acid substance containing a gene to be delivered into the nucleus of a cell, an importin protein (for example, importin-.beta.) capable of passing through the nuclear pore and involved in the nuclear transport, and a binding substance (for example, polyethyleneimine) bound to both of the nucleic acid substance and the importin protein. Nucleic acid transport from outside of a cell into the cell nucleus can be particularly promoted by administering the nucleic acid construct bound to a cell membrane receptor binding factor and/or a membrane fusing substance, or administering the nucleic acid construct encapsulated in a non-viral vector (for example, Sendai virus envelope) having cell membrane permeability and membrane fusing properties.