A multilayer block in which nanocrystalline alloy ribbon pieces are layered, the nanocrystalline alloy ribbon pieces, obtained by cutting nanocrystalline alloy ribbons into a strip shape, having a composition represented by the following Composition Formula: Fe 100-a-b-c-d B a Si b Cu c M d [Composition Formula] wherein, in Composition Formula, each of a, b, c, and d is an atomic percent; the expressions 13.0 ≤ a ≤ 17.0, 3.5 ≤ b ≤ 5.0, 0.6 ≤ c ≤ 1.1, and 0 ≤ d ≤ 0.5 are satisfied; and M represents at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, the nanocrystalline alloy ribbon pieces further comprising one or more impurities, the one or more impurities comprising a total of 0.4% by mass or less of one or more elements selected from Ni, Mn and Co, and a total of 1.5% by mass or less of one or more elements selected from the group consisting of Re, Zn, As, In, Sn and rare earth elements, and optionally one or more elements selected from O, S, P, Al, Ge, Ga, Be, Au and Ag, wherein the total content of the impurities in the nanocrystalline alloy ribbon piece is 1.5% by mass or less, wherein the nanocrystalline alloy ribbon encompasses not only an alloy ribbon which consists of only nanocrystals, but also an alloy ribbon in which nanocrystals are dispersed in an amorphous phase, and each of the nanocrystalline alloy ribbon pieces contains nanocrystal grains having a grain size of from 1 nm to 30 nm in an amount of from 30% by volume to 60% by volume, and has a thickness of from 10 μm to 30 μm, a width of from 5 mm to 100 mm, and a ratio of length to width of from 1 to 10, characterized in that the space factor is from 85% to 92%, wherein the space factor is calculate as indicated in the description. wherein, in Composition Formula, each of a, b, c, and d is an atomic percent; the expressions 13.0 ≤ a ≤ 17.0, 3.5 ≤ b ≤ 5.0, 0.6 ≤ c ≤ 1.1, and 0 ≤ d ≤ 0.5 are satisfied; and M represents at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, the nanocrystalline alloy ribbon pieces further comprising one or more impurities, the one or more impurities comprising a total of 0.4% by mass or less of one or more elements selected from Ni, Mn and Co, and a total of 1.5% by mass or less of one or more elements selected from the group consisting of Re, Zn, As, In, Sn and rare earth elements, and optionally one or more elements selected from O, S, P, Al, Ge, Ga, Be, Au and Ag, wherein the total content of the impurities in the nanocrystalline alloy ribbon piece is 1.5% by mass or less, wherein the nanocrystalline alloy ribbon encompasses not only an alloy ribbon which consists of only nanocrystals, but also an alloy ribbon in which nanocrystals are dispersed in an amorphous phase, and each of the nanocrystalline alloy ribbon pieces contains nanocrystal grains having a grain size of from 1 nm to 30 nm in an amount of from 30% by volume to 60% by volume, and has a thickness of from 10 μm to 30 μm, a width of from 5 mm to 100 mm, and a ratio of length to width of from 1 to 10, characterized in that the space factor is from 85% to 92%, wherein the space factor is calculate as indicated in the description.