To provide a medium binding device which is miniaturized at a low cost without increasing the number of components or complicating the device.

A tape is moved across a conveying means of a bank note bundle while making a half turn of a tape winding means 11 holding a fore end of the tape 2 at an initial position. The tape 2 extends in a blocking manner of the conveying path of the bank note bundle. Since the fore end of the bank note bundle conveyed by conveying belts 8 and 9 pushes the tape 2, the tape 2 covers the surface and back sides of the bank note bundle. Thereafter, the tape is moved across the conveying path of the bank note bundle while making the other half turn of the tape winding means 11, and the tape 2 is wound around the bank note bundle to bind the bank note bundle by conveying the bank note bundle in the reverse direction by the conveying belts 8 and 9.