A staple detection mechanism of an electric stapler in which wherein a passage 4 for inserting and withdrawing a staple cartridge 3 is formed in the magazine part 2 of a stapler body 1, a sheet staple a is stored in the staple cartridge 3, and the sheet staple a is driven out in order starting at a staple a1 at the front part of the sheet staple a after bending the staple from both sides, wherein a staple detection sensor 7 formed so that the both tip sides of an actuator 8 are converged is disposed so that the both side parts thereof face the access port of the passage 4 and are engaged with the upper or lower surface of the sheet staple a of the staple cartridge 3 having a tip part installed in the passage 4, and the actuator 8 is installed so as to be retractably rotated in the vertical direction relative to the longitudinal direction of the passage 4 and energized by a spring so as to be diagonally erected at all times.