An auxiliary fitting (10) is used in using a laminate terminal fitting (30) including interlocking portions (37) to be engaged with another terminal fitting placed on one surface side at a peripheral edge of an insertion hole (36), through which a fastening device (B) is insertable, without being assembled with the other terminal fitting. The interlocking portions (37) are so formed that plate surfaces are shifted toward the one surface side relative to other parts (48) and interlocking portions of the other terminal fitting are to be inserted into and engaged with recesses (38) formed at the other surface side of the interlocking portions (37). The auxiliary fitting (10) includes auxiliary inserting portions (12) to be inserted into the recesses (38) of the interlocking portions (37) and placed in contact with the interlocking portions (37).