To provide a staple driving machine which hardly causes buckling in a leg of a staple in driving.

The driving machine comprises an injection part 20 having an inner wall that forms an injection passage 28 which allows a driver blade 12 to strike a staple 5 and to drive the staple 5 into a member W. The inner wall of the injection part 20 comprises an inner wall part 28b for a head passage for allowing a top surface head 5d of the staple 5 to be passed therethrough and an inner wall part 28a for a pair of leg passages that are continuously formed at both ends of the inner wall part 28b for the head passage and allow the pair of legs 5e of the staple 5 to be passed therethrough. A leg deformation preventing part 40 having a protruded part 41 (an arm 30) protruded in at least a part of the injection passage 28 is provided in the inner wall part 28b for the head passage. The above constitution can prevent the staple 5 having a relatively long leg from being buckled in driving.