Abstract: There have been various conjectures on the kind of telescope produced and used by the Jesuit missionary Adam Schall von Bell(1591—1666) in the late Ming and early Qing Dynasties. Based on the accounts in historical documents together with simulated experiments conducted by the authors in a physics laboratory, we conclude that the said optical instrument was neither a camera obscura nor a Keplerian telescope, and that judging from its structure, it was essentially a Galilean telescope.