A staple gun includes: a casing having a front blocking surface; a magazine disposed in the casing; and a staple delivery element and a resilient element disposed at the magazine. The magazine includes at least a staple cutting portion each having a top surface, a front end surface, and a guiding surface connected between the top surface and the front end surface. The front end surface and the guiding surface face the front blocking surface. A clearance for passing staples is disposed between the front end surface and the front blocking surface. The staple delivery element pushes staples in the magazine in a staple delivering direction. The resilient element enables staples to push the front end surface and the guiding surface of the staple cutting portion of the magazine, such that the magazine moves relative to the casing in a clearance adjustment direction opposite to the staple delivering direction.