A cassette for stapler capable of storing staples with different lengths of needle legs and capable of being manufactured at a low cost, comprising a cassette body formed slender with a channel shaped cross section and having a staple extrusion groove provided at the tip thereof, a staple holder longitudinally fitted to the cassette body to hold the large number of staples, a feeder for moving the staples pressingly toward the tip thereof, a spring for energizing the feeder, and a guide rod for guiding the movement of the feeder, wherein a guide wall capable of storing the staples with different lengths of needles is provided in the staple holder.