To provide a lapping base board which can execute the stable lapping by fining crystal structure affected to particularly the lapping characteristic, related to an Sn base soft metal-made lapping base board.

In the lapping base board produced by melting and casting, molten metal consisting essentially of Sn or Sn mixed with one or more kinds of alloy elements among Zu, Cd, Pb, Sb, Bi belonging to the sub-groups from the II group to the V group in the periodic table is cast, and after cooling, the working at 20-90% working ratio is applied to induce the recrystallization by releasing the internal strain for a short time, and the mixed rate of the alloy elements is 0.1-10wt.% in total, and the average crystal grain diameter is ≤1mm, and after working, further, the recrystal stabilizing treatment is applied in the temp. range of (0.3-0.8)TM (m.p.).