Three new sesquiterpenoids, 3α, 4α-oxidoagarofuran, 3β, 4β-oxidoagarofuran, 3β, 4β-oxidoagarofuran and Δ^{9 (10)}-eremophilen-11-ol, as well as 10-epi-γ-eudesmol, 4α-hydroxydihydroagarofuran, α-agarofuran, dihydroagarofuran and β-eudesmol were isolated from the rhizome of Alpinia japonica. Their structures were determined by chemical and spectroscopic methods. It is interesting from a biogenetic point of view that Δ^{9 (10)}-eremophilen-11-ol, β-eudesmol and agarofurans which possess the 10-epimeric eudesmane carbon skeleton were all contained in the same plant.