A staple feeding mechanism includes the components of only a magazine with a pair of guides and spring receiver being integrated, a driving shaft having a double function and a staple feeding member (inclusive of the feeding nail and spring) movably arranged in the magazine. The feeding nail of the staple feeding member at the home position is lowered by the driving shaft and retracted from the staple cartridge. For this reason, the loading/unloading of the staple cartridge can be done without any hitch. The staple feeding mechanism only requires a necessary minimized number of components and so is simple in structure. Thus, the stapler can be provided at low cost. Particularly, the driving shaft necessary to cause the magazine to make a reciprocating motion is also used as a fulcrum member, thus requiring no new component. This further reduces the number of necessary components and also contributes to space saving.