Lawn mower

1. A lawn mower comprising:

a power supply;

a chassis for holding the power supply;

a fixed shaft attached to the chassis;

a rotary blade which is rotatably supported with respect to the fixed shaft;

a transmitting portion which transmits rotation of the power supply to the rotary blade;

a fixed blade which is coaxially-arranged with the rotary blade;

an elastic member which presses the rotary blade toward the fixed blade; and

a positioning portion which is configured to:

vary a position of the rotary blade relative to the fixed blade in an axial direction of the fixed shaft, and

regulate movement of the rotary blade toward a biasing direction of the elastic member at a plurality of positions, wherein:

a distance between the rotary blade and the fixed blade can be varied by operating the positioning portion,

the positioning portion is configured to set the position of the rotary blade in at least a first position and a second position,

in the first position, the rotary blade strongly contacts with the fixed blade, and

in the second position, the rotary blade weakly contacts with the fixed blade or does not contact with the fixed blade,

the fixed shaft is a hollow member through which a rod penetrates, and a part of the rod is connected to the positioning portion,

the position of the rotary blade in the axial direction of the fixed shaft is determined by the rod, and

a position of the rod in an axial direction thereof is determined by the positioning portion.

2. The lawn mower according to claim 1 ,

wherein the rotary blade and the fixed blade are arranged substantially parallel to the ground, and

wherein the rotary blade is disposed above the fixed blade.

3. The lawn mower according to claim 1 ,

wherein the positioning portion includes an operating lever, and

wherein the operating lever is provided at a position operable from an outside of a cover which covers the chassis.

4. The lawn mower according to claim 3 ,

wherein a plurality of pairs, each of which including the rotary blade and the fixed blade, are arranged in a lateral direction.

5. The lawn mower according to claim 4 ,

wherein the rotary blades included in the plurality of pairs are moved in the axial direction of the fixed shaft by operating the operating lever.