A blinding device for indicating the amount of negative pressure suction to use in a blinding operation to treat hemorrohids. The device is simple and convenient to use, and allows for more accurate binding operations. The binding device has a shell (100), a push tube (101) at the shell's (100) front end, and a suction tube (200) in the push tube (101). A negative pressure device (300) is in the shell (100). A scale cylinder (400) has a cylinder body (410) divided into two cavities (430a,430b) and a piston piece (420) within. The negative pressure device (300) has a suction port (310) in communication with the rear end of the suction tube (200) and connected with one of the cylinder cavities (430a, 430b). The cylinder body (410) can move relative to the shell (100), and the shell (100) has a scale part (500) corresponding to the moving displacement of the cylinder body (410). The elastic ring (600) is sleeved at the front end of the suction tube (200).