A method for preparing B cells which produce a human-type antibody, wherein the B cells are derived from a DT40 chicken B cell line capable of inducing or halting AID (activation induced cytidine deaminase) expression with the induction of the expression of an exogenous Cre recombinase gene through extracellular stimulation followed by the inversion of the direction of the exogenous AID gene by expressed Cre recombinase, the B cells are characterized in that: 1) the endogenous AID gene is functionally disrupted, and an AID protein resulting from the expression of the endogenous AID gene is not produced; 2) the B cells have an exogenous AID gene that is flanked by two loxP sequences in opposite directions to each other, and a promoter that is present upstream of the region flanked by the two loxP sequences and is capable of functioning in the animal cells, when the AID gene is placed in a forward direction with respect to the promoter, the AID gene can be expressed by the promoter, and when the AID gene is placed in a reverse direction with respect to the promoter, the expression of the AID gene is halted; and 3) a Cre recombinase gene is introduced so that Cre recombinase activation by extracellular stimulation is possible, and the direction of the region flanked by the two loxP sequences, which contains the exogenous AID gene, is inverted by Cre recombinase activation, and the B cells are further characterized in that: (i) only a constant region of an antibody gene of the B cells is substituted with a human antibody constant region gene; (ii) in the case of the heavy chain, the region from the CH1 region to a secretory exon encoding the constant region is substituted with a human-derived IgG antibody heavy chain constant region, and in the case of the light chain, only the constant region exon is substituted with a human-derived κ light chain constant region gene; and (iii) B cells producing a human-type antibody contain a splicing receptor sequence and a splicing branch point sequence, which are derived from a human antibody gene, in an intron that is present upstream of the human constant region gene, further contain as a polyA addition sequence downstream of the constant region gene, a polyA addition sequence of DT40-SW cells that are B cells derived from the DT40 chicken B cell line, and further contain a drug resistance gene flanked by loxP sequences upstream of the human constant region gene containing a splicing sequence. 1) the endogenous AID gene is functionally disrupted, and an AID protein resulting from the expression of the endogenous AID gene is not produced; 2) the B cells have an exogenous AID gene that is flanked by two loxP sequences in opposite directions to each other, and a promoter that is present upstream of the region flanked by the two loxP sequences and is capable of functioning in the animal cells, when the AID gene is placed in a forward direction with respect to the promoter, the AID gene can be expressed by the promoter, and when the AID gene is placed in a reverse direction with respect to the promoter, the expression of the AID gene is halted; and 3) a Cre recombinase gene is introduced so that Cre recombinase activation by extracellular stimulation is possible, and the direction of the region flanked by the two loxP sequences, which contains the exogenous AID gene, is inverted by Cre recombinase activation, and the B cells are further characterized in that: (i) only a constant region of an antibody gene of the B cells is substituted with a human antibody constant region gene; (ii) in the case of the heavy chain, the region from the CH1 region to a secretory exon encoding the constant region is substituted with a human-derived IgG antibody heavy chain constant region, and in the case of the light chain, only the constant region exon is substituted with a human-derived κ light chain constant region gene; and (iii) B cells producing a human-type antibody contain a splicing receptor sequence and a splicing branch point sequence, which are derived from a human antibody gene, in an intron that is present upstream of the human constant region gene, further contain as a polyA addition sequence downstream of the constant region gene, a polyA addition sequence of DT40-SW cells that are B cells derived from the DT40 chicken B cell line, and further contain a drug resistance gene flanked by loxP sequences upstream of the human constant region gene containing a splicing sequence. (i) only a constant region of an antibody gene of the B cells is substituted with a human antibody constant region gene; (ii) in the case of the heavy chain, the region from the CH1 region to a secretory exon encoding the constant region is substituted with a human-derived IgG antibody heavy chain constant region, and in the case of the light chain, only the constant region exon is substituted with a human-derived κ light chain constant region gene; and (iii) B cells producing a human-type antibody contain a splicing receptor sequence and a splicing branch point sequence, which are derived from a human antibody gene, in an intron that is present upstream of the human constant region gene, further contain as a polyA addition sequence downstream of the constant region gene, a polyA addition sequence of DT40-SW cells that are B cells derived from the DT40 chicken B cell line, and further contain a drug resistance gene flanked by loxP sequences upstream of the human constant region gene containing a splicing sequence.