Provided are a B cell-derived iPS cell generated using a convenient technique, a technology for providing a human antibody at low cost using the iPS cell, an immunologically humanized mouse prepared using cells differentiated from the iPS cell, and the like. Also provided are a cloned cell obtained by contacting a B cell with nuclear reprogramming factors excluding C/EBPα and Pax5 expression inhibiting substances, particularly nucleic acids that encode Oct3/4, Sox2, Klf4 and c-Myc, wherein the cloned cell has an immunoglobulin gene rearranged therein and possesses pluripotency and replication competence (B-iPS cell). Still also provided are a method of producing a monoclonal antibody against a specified antigen, comprising recovering an antibody from a culture of B cells obtained by differentiating a B-iPS cell derived from a B cell immunized with the specified antigen, and a method of generating an immunologically humanized mouse, comprising transplanting to an immunodeficient mouse a human immunohematological system cell obtained by differentiating a B-iPS cell.
