Abstract: A stapler for paper binding utilizes a supporting means to firmly support staples so as to make binding process easy and stable. A stapler of the present invention includes a pressure plate spring received in a pressure bar pivoted to a front-opened cartridge. The pressure plate spring includes a front striking plate and a front bumper to drive a staple for binding papers and to confine such a staple from forward inclination. A supporting wedge is received in the staple cartridge to slide in the front and to firmly support the staple which is driven downward for binding papers. Through the support of the supporting wedge and the front bumper of the striking plate of the pressure plate spring, staple is protected to straightly strike downward for binding papers efficiently.