The utility model discloses a capturing device for the vertical state of a levelling staff of a staff or surveyor pole. The capturing device is high in resolution, precision and reliability. The capturing device is provided with a casing (1), wherein a metal wire (2) suspended at the top end of the casing (1) is arranged in the casing (1); the lower end of the metal wire (2) is connected with a plumb bob (3); a metal ring is also arranged in the casing (1); the metal wire (2) and the metal ring are respectively connected to an alarming circuit; the metal ring is positioned above the plumb bob (3); the metal wire (2) is arranged in the metal ring; the metal ring is formed by butting two symmetrical metal strips (4); two push-pull devices (5) which are connected with the metal strips (4) and can drive the metal strips (4) to move oppositely or reversely are fixed on the casing (1).