We study the spectrum of 12ΛBe by using an extended version of antisymmetrized molecular dynamics for hypernuclei. Our result indicates that the Λ-particle impurity effect causes the positive-parity ground state of 12ΛBe to revert to the normal state, i.e., negative parity. This parity reversion is attributed to the difference in the Λ binding energy between the positive- and negative-parity states, which in turn originates in the difference in α clustering and deformation.
