Structure of the triaxially deformed hypernucleus <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mi>Mg</mml:mi> <mml:mprescripts/> <mml:mi mathvariant="normal">Λ</mml:mi> <mml:mn>27</mml:mn> </mml:mmultiscripts> </

The excitation spectra of $_{\mathrm{\ensuremath{\Lambda}}}^{27}\mathrm{Mg}$ as well as $^{26}\mathrm{Mg}$ are investigated within the framework of antisymmetrized molecular dynamics. In $^{26}\mathrm{Mg}$, it is found that the ground (${K}^{\ensuremath{\pi}}={0}^{+}$) and side (${K}^{\ensuremath{\pi}}={2}^{+}$) bands exhibit triaxial deformation. In addition to these bands, I also obtain three positive-parity bands with different nuclear quadrupole deformations in $^{26}\mathrm{Mg}$, whose energies and transition probabilities are consistent with observations. In $_{\mathrm{\ensuremath{\Lambda}}}^{27}\mathrm{Mg}$, five bands are predicted by the addition of a $\mathrm{\ensuremath{\Lambda}}$ particle in $s$ wave, corresponding to those in $^{26}\mathrm{Mg}$. In contrast, the coupling of a $\mathrm{\ensuremath{\Lambda}}$ particle in $p$ wave to the positive-parity states in $^{26}\mathrm{Mg}$ gives rise to a large number of excited states. These states can be classified into three groups having different spatial distributions of the $\mathrm{\ensuremath{\Lambda}}$ particle due to the triaxial deformation of the core nucleus $^{26}\mathrm{Mg}$.