[en] A spectroscopic study of Λ hypernuclei by the (π⁺, K⁺) reaction has been performed for the wide hypernuclear mass range using a new superconducting kaon spectrometer (INS-SKS) at the KEK 12 GeV PS. A _Λ¹²C spectrum with 2 MeV (FWHM) energy resolution was measured and core excited states of _Λ¹²C were clearly identified for the first time. It is discussed that the excitation energies and cross sections of these states will be closely related with the choice of ΛN interaction models as well as hypernuclear structure. Hypernuclear spectra of _Λ¹⁰B, _Λ²⁸Si, _Λ⁸⁹Y, _Λ¹³⁹La and _Λ²⁰⁸Pb were also obtained and binding energies of a Λ hyperon were deduced for each Λ orbital. The mass number dependence of the Λ binding energies is, within the present experimental errors, consistent with a calculation based on the Woods-Saxon potential