To provide a cell that can be applied in in-vitro cell differentiation system other than ES cells and has the deleted or inhibited expression functions of a normal gene (a wild type gene) in the allele corresponding to a trapped gene, a method for producing the cell, a gene-trapping method using the cell and an anti-sense promoter-introduced vector to be used for preparing the cell.

The trap clone can efficiently be obtain by transducing a gene trap vector into a cell. Additionally, an antisense RNA to the trapped gene is forcibly transferred and the transferred products from the wild type gene is broken by transducing an antisense promoter-introduced vector that can insert a strong promoter into the endogenous gene in the opposite direction in the prescribed position of the mutant gene locus where the transduction of the gene trap vector of the trapped gene is occurred.