To solve the problem of conventional straw cutters having disadvantageously preset cut lengths of discharged straw, restricted to two kinds of a long length and a short length.

The straw cutter 1 for cutting charged waste straws includes a pair of rotary shafts 10, 20 rotating in opposite directions to each other and a plurality of rotary blades 11, 21 attached to the rotary shafts 10, 20 at given intervals, respectively. Each of the rotary shafts 10, 20 is a screw shaft having an oval cross-section. The rotary blades 11, 21 are penetrated with the rotary shafts 10, 20 in a manner slidable in axial direction and unable to rotate relative to each other, and are fixed with screw nuts 7a, 7b from both sides.