Abstract: A stapler includes left and right shells, a front shell, a staple magazine, an urging plate and a controlling switch. The left and right shells are connected with each other, such that a receiving space is defined therebetween. The front shell is connected with front portions of the left and right shells and provided with an opening in communication with the receiving space. The staple magazine is detachably disposed in the receiving space and the urging plate is disposed in front of the staple magazine. The controlling switch is reciprocally slidably disposed in the opening of the front shell and adapted to adjust a gap between the staple magazine and the urging plate for fitting various staples having different thickness. Because the front side of the front shell is seamless without connective joint, the stapler is strong in structure and durable in use.